From dd2d601081b649c942f14fdb1609f2baf66bdc73 Mon Sep 17 00:00:00 2001
From: Brian Picciano <mediocregopher@gmail.com>
Date: Sat, 15 Jun 2019 16:45:53 -0600
Subject: [PATCH] mcfg: refactor so as to use new mcmp.Component type, and use
 the option pattern to reduce number of arguments to parameters

---
 mcfg/cli.go         | 154 ++++++++++++++-------------
 mcfg/cli_test.go    | 152 +++++++++++++-------------
 mcfg/env.go         |  28 ++---
 mcfg/env_test.go    |   4 +-
 mcfg/mcfg.go        |  64 +++++------
 mcfg/mcfg_test.go   |  33 +++---
 mcfg/param.go       | 252 ++++++++++++++++++++++----------------------
 mcfg/source.go      |  30 +++---
 mcfg/source_test.go |  81 ++++++--------
 9 files changed, 399 insertions(+), 399 deletions(-)

diff --git a/mcfg/cli.go b/mcfg/cli.go
index 13e8df6..e8c7b4f 100644
--- a/mcfg/cli.go
+++ b/mcfg/cli.go
@@ -1,7 +1,6 @@
 package mcfg
 
 import (
-	"context"
 	"fmt"
 	"io"
 	"os"
@@ -9,6 +8,7 @@ import (
 	"sort"
 	"strings"
 
+	"github.com/mediocregopher/mediocre-go-lib/mcmp"
 	"github.com/mediocregopher/mediocre-go-lib/mctx"
 	"github.com/mediocregopher/mediocre-go-lib/merr"
 )
@@ -25,64 +25,76 @@ type cliTail struct {
 	descr string
 }
 
-// WithCLITail returns a Context which modifies the behavior of SourceCLI's
-// Parse. Normally when SourceCLI encounters an unexpected Arg it will
-// immediately return an error. This function modifies the Context to indicate
-// to Parse that the unexpected Arg, and all subsequent Args (i.e. the tail),
-// should be set to the returned []string value.
+// CLITail modifies the behavior of SourceCLI's Parse. Normally when SourceCLI
+// encounters an unexpected Arg it will immediately return an error. This
+// function modifies the Component to indicate to Parse that the unexpected Arg,
+// and all subsequent Args (i.e. the tail), should be set to the returned
+// []string value.
 //
 // The descr (optional) will be appended to the "Usage" line which is printed
 // with the help document when "-h" is passed in.
-func WithCLITail(ctx context.Context, descr string) (context.Context, *[]string) {
-	if ctx.Value(cliKeyTail) != nil {
-		panic("WithCLITail already called in this Context")
+//
+// This function panics if not called on a root Component (i.e. a Component
+// which has no parents).
+func CLITail(cmp *mcmp.Component, descr string) *[]string {
+	if len(cmp.Path()) != 0 {
+		panic("CLITail can only be used on a root Component")
 	}
+
 	tailPtr := new([]string)
-	ctx = context.WithValue(ctx, cliKeyTail, cliTail{
+	cmp.SetValue(cliKeyTail, cliTail{
 		dst:   tailPtr,
 		descr: descr,
 	})
-	return ctx, tailPtr
+	return tailPtr
 }
 
-func populateCLITail(ctx context.Context, tail []string) bool {
-	ct, ok := ctx.Value(cliKeyTail).(cliTail)
+func populateCLITail(cmp *mcmp.Component, tail []string) bool {
+	ct, ok := cmp.Value(cliKeyTail).(cliTail)
 	if ok {
 		*ct.dst = tail
 	}
 	return ok
 }
 
-func getCLITailDescr(ctx context.Context) string {
-	ct, _ := ctx.Value(cliKeyTail).(cliTail)
+func getCLITailDescr(cmp *mcmp.Component) string {
+	ct, _ := cmp.Value(cliKeyTail).(cliTail)
 	return ct.descr
 }
 
 type subCmd struct {
 	name, descr string
 	flag        *bool
-	callback    func(context.Context) context.Context
+	callback    func(*mcmp.Component)
 }
 
-// WithCLISubCommand establishes a sub-command which can be activated on the
+// CLISubCommand establishes a sub-command which can be activated on the
 // command-line. When a sub-command is given on the command-line, the bool
 // returned for that sub-command will be set to true.
 //
-// Additionally, the Context which was passed into Parse (i.e. the one passed
-// into Populate) will be passed into the given callback, and the returned one
-// used for subsequent parsing. This allows for setting sub-command specific
-// Params, sub-command specific runtime behavior (via mrun.WithStartHook),
-// support for sub-sub-commands, and more. The callback may be nil.
+// Additionally, the Component which was passed into Parse (i.e. the one passed
+// into Populate) will be passed into the given callback, and can be modified
+// for subsequent parsing. This allows for setting sub-command specific Params,
+// sub-command specific runtime behavior (via mrun.WithStartHook), support for
+// sub-sub-commands, and more. The callback may be nil.
 //
-// If any sub-commands have been defined on a Context which is passed into
+// If any sub-commands have been defined on a Component which is passed into
 // Parse, it is assumed that a sub-command is required on the command-line.
 //
-// Sub-commands must be specified before any other options on the command-line.
-func WithCLISubCommand(ctx context.Context, name, descr string, callback func(context.Context) context.Context) (context.Context, *bool) {
-	m, _ := ctx.Value(cliKeySubCmdM).(map[string]subCmd)
+// When parsing the command-line options, it is assumed that sub-commands will
+// be found before any other options.
+//
+// This function panics if not called on a root Component (i.e. a Component
+// which has no parents).
+func CLISubCommand(cmp *mcmp.Component, name, descr string, callback func(*mcmp.Component)) *bool {
+	if len(cmp.Path()) != 0 {
+		panic("CLISubCommand can only be used on a root Component")
+	}
+
+	m, _ := cmp.Value(cliKeySubCmdM).(map[string]subCmd)
 	if m == nil {
 		m = map[string]subCmd{}
-		ctx = context.WithValue(ctx, cliKeySubCmdM, m)
+		cmp.SetValue(cliKeySubCmdM, m)
 	}
 
 	flag := new(bool)
@@ -92,7 +104,7 @@ func WithCLISubCommand(ctx context.Context, name, descr string, callback func(co
 		flag:     flag,
 		callback: callback,
 	}
-	return ctx, flag
+	return flag
 }
 
 // SourceCLI is a Source which will parse configuration from the CLI.
@@ -100,27 +112,30 @@ func WithCLISubCommand(ctx context.Context, name, descr string, callback func(co
 // Possible CLI options are generated by joining a Param's Path and Name with
 // dashes. For example:
 //
-//	ctx := mctx.New()
-//	ctx = mctx.ChildOf(ctx, "foo")
-//	ctx = mctx.ChildOf(ctx, "bar")
-//	addr := mcfg.String(ctx, "addr", "", "Some address")
+//	cmp := new(mcmp.Component)
+//	cmpFoo = cmp.Child("foo")
+//	cmpFooBar = foo.Child("bar")
+//	addr := mcfg.String(cmpFooBar, "addr", "", "Some address")
 //	// the CLI option to fill addr will be "--foo-bar-addr"
 //
-// If the "-h" option is seen then a help page will be printed to
-// stdout and the process will exit. Since all normally-defined parameters must
-// being with double-dash ("--") they won't ever conflict with the help option.
+// If the "-h" option is seen then a help page will be printed to stdout and the
+// process will exit. Since all normally-defined parameters must being with
+// double-dash ("--") they won't ever conflict with the help option.
 //
 // SourceCLI behaves a little differently with boolean parameters. Setting the
-// value of a boolean parameter directly _must_ be done with an equals, for
-// example: `--boolean-flag=1` or `--boolean-flag=false`. Using the
-// space-separated format will not work. If a boolean has no equal-separated
-// value it is assumed to be setting the value to `true`, as would be expected.
+// value of a boolean parameter directly _must_ be done with an equals, or with
+// no value at all. For example: `--boolean-flag`, `--boolean-flag=1` or
+// `--boolean-flag=false`.  Using the space-separated format will not work. If a
+// boolean has no equal-separated value it is assumed to be setting the value to
+// `true`.
 type SourceCLI struct {
 	Args []string // if nil then os.Args[1:] is used
 
 	DisableHelpPage bool
 }
 
+var _ Source = new(SourceCLI)
+
 const (
 	cliKeyJoin   = "-"
 	cliKeyPrefix = "--"
@@ -128,51 +143,51 @@ const (
 	cliHelpArg   = "-h"
 )
 
-// Parse implements the method for the Source interface
-func (cli *SourceCLI) Parse(ctx context.Context) (context.Context, []ParamValue, error) {
+// Parse implements the method for the Source interface.
+func (cli *SourceCLI) Parse(cmp *mcmp.Component) ([]ParamValue, error) {
 	args := cli.Args
 	if cli.Args == nil {
 		args = os.Args[1:]
 	}
-	return cli.parse(ctx, nil, args)
+	return cli.parse(cmp, nil, args)
 }
 
 func (cli *SourceCLI) parse(
-	ctx context.Context,
+	cmp *mcmp.Component,
 	subCmdPrefix, args []string,
 ) (
-	context.Context,
 	[]ParamValue,
 	error,
 ) {
-	pM, err := cli.cliParams(CollectParams(ctx))
+	pM, err := cli.cliParams(CollectParams(cmp))
 	if err != nil {
-		return nil, nil, err
+		return nil, err
 	}
 
 	printHelpAndExit := func() {
-		cli.printHelp(ctx, os.Stderr, subCmdPrefix, pM)
+		// TODO check DisableHelpPage here?
+		cli.printHelp(cmp, os.Stderr, subCmdPrefix, pM)
 		os.Stderr.Sync()
 		os.Exit(1)
 	}
 
-	// if sub-commands were defined on this Context then handle that first. One
-	// of them should have been given, in which case send the Context through
-	// the callback to obtain a new one (which presumably has further config
-	// options the previous didn't) and call parse again.
-	subCmdM, _ := ctx.Value(cliKeySubCmdM).(map[string]subCmd)
+	// if sub-commands were defined on this Component then handle that first.
+	// One of them should have been given, in which case send the Context
+	// through the callback to obtain a new one (which presumably has further
+	// config options the previous didn't) and call parse again.
+	subCmdM, _ := cmp.Value(cliKeySubCmdM).(map[string]subCmd)
 	if len(subCmdM) > 0 {
 		subCmd, args, ok := cli.getSubCmd(subCmdM, args)
 		if !ok {
 			printHelpAndExit()
 		}
-		ctx = context.WithValue(ctx, cliKeySubCmdM, nil)
+		cmp.SetValue(cliKeySubCmdM, nil)
 		if subCmd.callback != nil {
-			ctx = subCmd.callback(ctx)
+			subCmd.callback(cmp)
 		}
 		subCmdPrefix = append(subCmdPrefix, subCmd.name)
 		*subCmd.flag = true
-		return cli.parse(ctx, subCmdPrefix, args)
+		return cli.parse(cmp, subCmdPrefix, args)
 	}
 
 	// if sub-commands were not set, then proceed with normal command-line arg
@@ -208,11 +223,11 @@ func (cli *SourceCLI) parse(
 				break
 			}
 			if !pOk {
-				if ok := populateCLITail(ctx, args[i:]); ok {
-					return ctx, pvs, nil
+				if ok := populateCLITail(cmp, args[i:]); ok {
+					return pvs, nil
 				}
-				ctx := mctx.Annotate(context.Background(), "param", arg)
-				return nil, nil, merr.New("unexpected config parameter", ctx)
+				return nil, merr.New("unexpected config parameter",
+					mctx.Annotated("param", arg))
 			}
 		}
 
@@ -231,7 +246,7 @@ func (cli *SourceCLI) parse(
 
 		pvs = append(pvs, ParamValue{
 			Name:  p.Name,
-			Path:  mctx.Path(p.Context),
+			Path:  p.Component.Path(),
 			Value: p.fuzzyParse(pvStrVal),
 		})
 
@@ -242,11 +257,11 @@ func (cli *SourceCLI) parse(
 		pvStrValOk = false
 	}
 	if pOk && !pvStrValOk {
-		ctx := mctx.Annotate(p.Context, "param", key)
-		return nil, nil, merr.New("param expected a value", ctx)
+		ctx := mctx.Annotate(p.Component.Annotated(), "param", key)
+		return nil, merr.New("param expected a value", ctx)
 	}
 
-	return ctx, pvs, nil
+	return pvs, nil
 }
 
 func (cli *SourceCLI) getSubCmd(subCmdM map[string]subCmd, args []string) (subCmd, []string, bool) {
@@ -265,14 +280,14 @@ func (cli *SourceCLI) getSubCmd(subCmdM map[string]subCmd, args []string) (subCm
 func (cli *SourceCLI) cliParams(params []Param) (map[string]Param, error) {
 	m := map[string]Param{}
 	for _, p := range params {
-		key := strings.Join(append(mctx.Path(p.Context), p.Name), cliKeyJoin)
+		key := strings.Join(append(p.Component.Path(), p.Name), cliKeyJoin)
 		m[cliKeyPrefix+key] = p
 	}
 	return m, nil
 }
 
 func (cli *SourceCLI) printHelp(
-	ctx context.Context,
+	cmp *mcmp.Component,
 	w io.Writer,
 	subCmdPrefix []string,
 	pM map[string]Param,
@@ -313,7 +328,7 @@ func (cli *SourceCLI) printHelp(
 		subCmd
 	}
 
-	subCmdM, _ := ctx.Value(cliKeySubCmdM).(map[string]subCmd)
+	subCmdM, _ := cmp.Value(cliKeySubCmdM).(map[string]subCmd)
 	subCmdA := make([]subCmdEntry, 0, len(subCmdM))
 	for name, subCmd := range subCmdM {
 		subCmdA = append(subCmdA, subCmdEntry{name: name, subCmd: subCmd})
@@ -333,7 +348,7 @@ func (cli *SourceCLI) printHelp(
 	if len(pA) > 0 {
 		fmt.Fprint(w, " [options]")
 	}
-	if descr := getCLITailDescr(ctx); descr != "" {
+	if descr := getCLITailDescr(cmp); descr != "" {
 		fmt.Fprintf(w, " %s", descr)
 	}
 	fmt.Fprint(w, "\n\n")
@@ -359,11 +374,6 @@ func (cli *SourceCLI) printHelp(
 			}
 			fmt.Fprint(w, "\n")
 			if usage := p.Usage; usage != "" {
-				// make all usages end with a period, because I say so
-				usage = strings.TrimSpace(usage)
-				if !strings.HasSuffix(usage, ".") {
-					usage += "."
-				}
 				fmt.Fprintln(w, "\t\t"+usage)
 			}
 			fmt.Fprint(w, "\n")
diff --git a/mcfg/cli_test.go b/mcfg/cli_test.go
index 9381ac3..12818c8 100644
--- a/mcfg/cli_test.go
+++ b/mcfg/cli_test.go
@@ -2,13 +2,13 @@ package mcfg
 
 import (
 	"bytes"
-	"context"
 	"fmt"
 	"regexp"
 	"strings"
 	. "testing"
 	"time"
 
+	"github.com/mediocregopher/mediocre-go-lib/mcmp"
 	"github.com/mediocregopher/mediocre-go-lib/mrand"
 	"github.com/mediocregopher/mediocre-go-lib/mtest/massert"
 	"github.com/mediocregopher/mediocre-go-lib/mtest/mchk"
@@ -17,37 +17,38 @@ import (
 )
 
 func TestSourceCLIHelp(t *T) {
-	assertHelp := func(ctx context.Context, subCmdPrefix []string, exp string) {
+	assertHelp := func(cmp *mcmp.Component, subCmdPrefix []string, exp string) {
 		buf := new(bytes.Buffer)
 		src := &SourceCLI{}
-		pM, err := src.cliParams(CollectParams(ctx))
+		pM, err := src.cliParams(CollectParams(cmp))
 		require.NoError(t, err)
-		src.printHelp(ctx, buf, subCmdPrefix, pM)
+		src.printHelp(cmp, buf, subCmdPrefix, pM)
 
 		out := buf.String()
 		ok := regexp.MustCompile(exp).MatchString(out)
 		assert.True(t, ok, "exp:%s (%q)\ngot:%s (%q)", exp, exp, out, out)
 	}
 
-	ctx := context.Background()
-	assertHelp(ctx, nil, `^Usage: \S+
+	cmp := new(mcmp.Component)
+	assertHelp(cmp, nil, `^Usage: \S+
 
 $`)
-	assertHelp(ctx, []string{"foo", "bar"}, `^Usage: \S+ foo bar
+	assertHelp(cmp, []string{"foo", "bar"}, `^Usage: \S+ foo bar
 
 $`)
 
-	ctx, _ = WithInt(ctx, "foo", 5, "Test int param  ") // trailing space should be trimmed
-	ctx, _ = WithBool(ctx, "bar", "Test bool param.")
-	ctx, _ = WithString(ctx, "baz", "baz", "Test string param")
-	ctx, _ = WithRequiredString(ctx, "baz2", "")
-	ctx, _ = WithRequiredString(ctx, "baz3", "")
+	Int(cmp, "foo", ParamDefault(5), ParamUsage("Test int param  ")) // trailing space should be trimmed
+	Bool(cmp, "bar", ParamUsage("Test bool param."))
+	String(cmp, "baz", ParamDefault("baz"), ParamUsage("Test string param"))
+	String(cmp, "baz2", ParamUsage("Required string param"), ParamRequired())
+	String(cmp, "baz3", ParamRequired())
 
-	assertHelp(ctx, nil, `^Usage: \S+ \[options\]
+	assertHelp(cmp, nil, `^Usage: \S+ \[options\]
 
 Options:
 
 	--baz2 \(Required\)
+		Required string param.
 
 	--baz3 \(Required\)
 
@@ -62,11 +63,12 @@ Options:
 
 $`)
 
-	assertHelp(ctx, []string{"foo", "bar"}, `^Usage: \S+ foo bar \[options\]
+	assertHelp(cmp, []string{"foo", "bar"}, `^Usage: \S+ foo bar \[options\]
 
 Options:
 
 	--baz2 \(Required\)
+		Required string param.
 
 	--baz3 \(Required\)
 
@@ -81,9 +83,9 @@ Options:
 
 $`)
 
-	ctx, _ = WithCLISubCommand(ctx, "first", "First sub-command", nil)
-	ctx, _ = WithCLISubCommand(ctx, "second", "Second sub-command", nil)
-	assertHelp(ctx, []string{"foo", "bar"}, `^Usage: \S+ foo bar <sub-command> \[options\]
+	CLISubCommand(cmp, "first", "First sub-command", nil)
+	CLISubCommand(cmp, "second", "Second sub-command", nil)
+	assertHelp(cmp, []string{"foo", "bar"}, `^Usage: \S+ foo bar <sub-command> \[options\]
 
 Sub-commands:
 
@@ -93,6 +95,7 @@ Sub-commands:
 Options:
 
 	--baz2 \(Required\)
+		Required string param.
 
 	--baz3 \(Required\)
 
@@ -107,8 +110,8 @@ Options:
 
 $`)
 
-	ctx, _ = WithCLITail(ctx, "[arg...]")
-	assertHelp(ctx, nil, `^Usage: \S+ <sub-command> \[options\] \[arg\.\.\.\]
+	CLITail(cmp, "[arg...]")
+	assertHelp(cmp, nil, `^Usage: \S+ <sub-command> \[options\] \[arg\.\.\.\]
 
 Sub-commands:
 
@@ -118,6 +121,7 @@ Sub-commands:
 Options:
 
 	--baz2 \(Required\)
+		Required string param.
 
 	--baz3 \(Required\)
 
@@ -165,11 +169,11 @@ func TestSourceCLI(t *T) {
 			s := ss.(state)
 			p := a.Params.(params)
 
-			s.srcCommonState = s.srcCommonState.applyCtxAndPV(p.srcCommonParams)
+			s.srcCommonState = s.srcCommonState.applyCmpAndPV(p.srcCommonParams)
 			if !p.unset {
 				arg := cliKeyPrefix
-				if len(p.path) > 0 {
-					arg += strings.Join(p.path, cliKeyJoin) + cliKeyJoin
+				if path := p.cmp.Path(); len(path) > 0 {
+					arg += strings.Join(path, cliKeyJoin) + cliKeyJoin
 				}
 				arg += p.name
 				if !p.isBool {
@@ -194,10 +198,10 @@ func TestSourceCLI(t *T) {
 	}
 }
 
-func TestWithCLITail(t *T) {
-	ctx := context.Background()
-	ctx, _ = WithInt(ctx, "foo", 5, "")
-	ctx, _ = WithBool(ctx, "bar", "")
+func TestCLITail(t *T) {
+	cmp := new(mcmp.Component)
+	Int(cmp, "foo", ParamDefault(5))
+	Bool(cmp, "bar")
 
 	type testCase struct {
 		args    []string
@@ -228,8 +232,8 @@ func TestWithCLITail(t *T) {
 	}
 
 	for _, tc := range cases {
-		ctx, tail := WithCLITail(ctx, "foo")
-		_, err := Populate(ctx, &SourceCLI{Args: tc.args})
+		tail := CLITail(cmp, "foo")
+		err := Populate(cmp, &SourceCLI{Args: tc.args})
 		massert.Require(t, massert.Comment(massert.All(
 			massert.Nil(err),
 			massert.Equal(tc.expTail, *tail),
@@ -237,13 +241,13 @@ func TestWithCLITail(t *T) {
 	}
 }
 
-func ExampleWithCLITail() {
-	ctx := context.Background()
-	ctx, foo := WithInt(ctx, "foo", 1, "Description of foo.")
-	ctx, tail := WithCLITail(ctx, "[arg...]")
-	ctx, bar := WithString(ctx, "bar", "defaultVal", "Description of bar.")
+func ExampleCLITail() {
+	cmp := new(mcmp.Component)
+	foo := Int(cmp, "foo", ParamDefault(1), ParamUsage("Description of foo."))
+	tail := CLITail(cmp, "[arg...]")
+	bar := String(cmp, "bar", ParamDefault("defaultVal"), ParamUsage("Description of bar."))
 
-	_, err := Populate(ctx, &SourceCLI{
+	err := Populate(cmp, &SourceCLI{
 		Args: []string{"--foo=100", "arg1", "arg2", "arg3"},
 	})
 
@@ -251,9 +255,9 @@ func ExampleWithCLITail() {
 	// Output: err:<nil> foo:100 bar:defaultVal tail:[]string{"arg1", "arg2", "arg3"}
 }
 
-func TestWithCLISubCommand(t *T) {
+func TestCLISubCommand(t *T) {
 	var (
-		ctx   context.Context
+		cmp   *mcmp.Component
 		foo   *int
 		bar   *int
 		baz   *int
@@ -262,22 +266,20 @@ func TestWithCLISubCommand(t *T) {
 	)
 	reset := func() {
 		foo, bar, baz, aFlag, bFlag = nil, nil, nil, nil, nil
-		ctx = context.Background()
-		ctx, foo = WithInt(ctx, "foo", 0, "Description of foo.")
-		ctx, aFlag = WithCLISubCommand(ctx, "a", "Description of a.",
-			func(ctx context.Context) context.Context {
-				ctx, bar = WithInt(ctx, "bar", 0, "Description of bar.")
-				return ctx
+		cmp = new(mcmp.Component)
+		foo = Int(cmp, "foo")
+		aFlag = CLISubCommand(cmp, "a", "Description of a.",
+			func(cmp *mcmp.Component) {
+				bar = Int(cmp, "bar")
 			})
-		ctx, bFlag = WithCLISubCommand(ctx, "b", "Description of b.",
-			func(ctx context.Context) context.Context {
-				ctx, baz = WithInt(ctx, "baz", 0, "Description of baz.")
-				return ctx
+		bFlag = CLISubCommand(cmp, "b", "Description of b.",
+			func(cmp *mcmp.Component) {
+				baz = Int(cmp, "baz")
 			})
 	}
 
 	reset()
-	_, err := Populate(ctx, &SourceCLI{
+	err := Populate(cmp, &SourceCLI{
 		Args: []string{"a", "--foo=1", "--bar=2"},
 	})
 	massert.Require(t,
@@ -290,7 +292,7 @@ func TestWithCLISubCommand(t *T) {
 	)
 
 	reset()
-	_, err = Populate(ctx, &SourceCLI{
+	err = Populate(cmp, &SourceCLI{
 		Args: []string{"b", "--foo=1", "--baz=3"},
 	})
 	massert.Require(t,
@@ -303,40 +305,48 @@ func TestWithCLISubCommand(t *T) {
 	)
 }
 
-func ExampleWithCLISubCommand() {
-	// Create a new Context with a parameter "foo", which can be used across all
-	// sub-commands.
-	ctx := context.Background()
-	ctx, foo := WithInt(ctx, "foo", 0, "Description of foo.")
+func ExampleCLISubCommand() {
+	var (
+		cmp           *mcmp.Component
+		foo, bar, baz *int
+		aFlag, bFlag  *bool
+	)
 
-	// Create a sub-command "a", which has a parameter "bar" specific to it.
-	var bar *int
-	ctx, aFlag := WithCLISubCommand(ctx, "a", "Description of a.",
-		func(ctx context.Context) context.Context {
-			ctx, bar = WithInt(ctx, "bar", 0, "Description of bar.")
-			return ctx
-		})
+	// resetExample re-initializes all variables used in this example. We'll
+	// call it multiple times to show different behaviors depending on what
+	// arguments are passed in.
+	resetExample := func() {
+		// Create a new Component with a parameter "foo", which can be used across
+		// all sub-commands.
+		cmp = new(mcmp.Component)
+		foo = Int(cmp, "foo")
 
-	// Create a sub-command "b", which has a parameter "baz" specific to it.
-	var baz *int
-	ctx, bFlag := WithCLISubCommand(ctx, "b", "Description of b.",
-		func(ctx context.Context) context.Context {
-			ctx, baz = WithInt(ctx, "baz", 0, "Description of baz.")
-			return ctx
-		})
+		// Create a sub-command "a", which has a parameter "bar" specific to it.
+		aFlag = CLISubCommand(cmp, "a", "Description of a.",
+			func(cmp *mcmp.Component) {
+				bar = Int(cmp, "bar")
+			})
+
+		// Create a sub-command "b", which has a parameter "baz" specific to it.
+		bFlag = CLISubCommand(cmp, "b", "Description of b.",
+			func(cmp *mcmp.Component) {
+				baz = Int(cmp, "baz")
+			})
+	}
 
 	// Use Populate with manually generated CLI arguments, calling the "a"
 	// sub-command.
+	resetExample()
 	args := []string{"a", "--foo=1", "--bar=2"}
-	if _, err := Populate(ctx, &SourceCLI{Args: args}); err != nil {
+	if err := Populate(cmp, &SourceCLI{Args: args}); err != nil {
 		panic(err)
 	}
 	fmt.Printf("foo:%d bar:%d aFlag:%v bFlag:%v\n", *foo, *bar, *aFlag, *bFlag)
 
-	// reset output for another Populate, this time calling the "b" sub-command.
-	*aFlag = false
+	// reset for another Populate, this time calling the "b" sub-command.
+	resetExample()
 	args = []string{"b", "--foo=1", "--baz=3"}
-	if _, err := Populate(ctx, &SourceCLI{Args: args}); err != nil {
+	if err := Populate(cmp, &SourceCLI{Args: args}); err != nil {
 		panic(err)
 	}
 	fmt.Printf("foo:%d baz:%d aFlag:%v bFlag:%v\n", *foo, *baz, *aFlag, *bFlag)
diff --git a/mcfg/env.go b/mcfg/env.go
index b94aec6..30b6c3e 100644
--- a/mcfg/env.go
+++ b/mcfg/env.go
@@ -1,10 +1,10 @@
 package mcfg
 
 import (
-	"context"
 	"os"
 	"strings"
 
+	"github.com/mediocregopher/mediocre-go-lib/mcmp"
 	"github.com/mediocregopher/mediocre-go-lib/mctx"
 	"github.com/mediocregopher/mediocre-go-lib/merr"
 )
@@ -16,10 +16,10 @@ import (
 // underscores and making all characters uppercase, as well as changing all
 // dashes to underscores.
 //
-//	ctx := mctx.New()
-//	ctx = mctx.ChildOf(ctx, "foo")
-//	ctx = mctx.ChildOf(ctx, "bar")
-//	addr := mcfg.String(ctx, "srv-addr", "", "Some address")
+//	cmp := new(mcmp.Component)
+//	cmpFoo := cmp.Child("foo")
+//	cmpFooBar := cmp.Child("bar")
+//	addr := mcfg.String(cmpFooBar, "srv-addr", "", "Some address")
 //	// the Env option to fill addr will be "FOO_BAR_SRV_ADDR"
 //
 type SourceEnv struct {
@@ -32,6 +32,8 @@ type SourceEnv struct {
 	Prefix string
 }
 
+var _ Source = new(SourceEnv)
+
 func (env *SourceEnv) expectedName(path []string, name string) string {
 	out := strings.Join(append(path, name), "_")
 	if env.Prefix != "" {
@@ -42,17 +44,17 @@ func (env *SourceEnv) expectedName(path []string, name string) string {
 	return out
 }
 
-// Parse implements the method for the Source interface
-func (env *SourceEnv) Parse(ctx context.Context) (context.Context, []ParamValue, error) {
+// Parse implements the method for the Source interface.
+func (env *SourceEnv) Parse(cmp *mcmp.Component) ([]ParamValue, error) {
 	kvs := env.Env
 	if kvs == nil {
 		kvs = os.Environ()
 	}
 
-	params := CollectParams(ctx)
+	params := CollectParams(cmp)
 	pM := map[string]Param{}
 	for _, p := range params {
-		name := env.expectedName(mctx.Path(p.Context), p.Name)
+		name := env.expectedName(p.Component.Path(), p.Name)
 		pM[name] = p
 	}
 
@@ -60,18 +62,18 @@ func (env *SourceEnv) Parse(ctx context.Context) (context.Context, []ParamValue,
 	for _, kv := range kvs {
 		split := strings.SplitN(kv, "=", 2)
 		if len(split) != 2 {
-			ctx := mctx.Annotate(context.Background(), "kv", kv)
-			return nil, nil, merr.New("malformed environment key/value pair", ctx)
+			return nil, merr.New("malformed environment key/value pair",
+				mctx.Annotated("kv", kv))
 		}
 		k, v := split[0], split[1]
 		if p, ok := pM[k]; ok {
 			pvs = append(pvs, ParamValue{
 				Name:  p.Name,
-				Path:  mctx.Path(p.Context),
+				Path:  p.Component.Path(),
 				Value: p.fuzzyParse(v),
 			})
 		}
 	}
 
-	return ctx, pvs, nil
+	return pvs, nil
 }
diff --git a/mcfg/env_test.go b/mcfg/env_test.go
index 17f1d49..9373b86 100644
--- a/mcfg/env_test.go
+++ b/mcfg/env_test.go
@@ -36,9 +36,9 @@ func TestSourceEnv(t *T) {
 		Apply: func(ss mchk.State, a mchk.Action) (mchk.State, error) {
 			s := ss.(state)
 			p := a.Params.(params)
-			s.srcCommonState = s.srcCommonState.applyCtxAndPV(p.srcCommonParams)
+			s.srcCommonState = s.srcCommonState.applyCmpAndPV(p.srcCommonParams)
 			if !p.unset {
-				kv := strings.Join(append(p.path, p.name), "_")
+				kv := strings.Join(append(p.cmp.Path(), p.name), "_")
 				kv = strings.Replace(kv, "-", "_", -1)
 				kv = strings.ToUpper(kv)
 				kv += "="
diff --git a/mcfg/mcfg.go b/mcfg/mcfg.go
index ff742cb..f834cb0 100644
--- a/mcfg/mcfg.go
+++ b/mcfg/mcfg.go
@@ -2,21 +2,18 @@
 // parameters and various methods of filling those parameters from external
 // configuration sources (e.g. the command line and environment variables).
 //
-// Parameters are registered onto a context, and that same context is used later
-// to collect and fulfill those parameters. When used with the mctx package's
-// child/parent context functionality, the path of a context is incorporated
-// into the parameter's full name in order to namespace parameters which exist
-// in different contexts.
+// Parameters are registered onto a Component, and that same Component (or one
+// of its ancestors) is used later to collect and fill those parameters.
 package mcfg
 
 import (
-	"context"
 	"crypto/md5"
 	"encoding/hex"
 	"encoding/json"
 	"fmt"
 	"sort"
 
+	"github.com/mediocregopher/mediocre-go-lib/mcmp"
 	"github.com/mediocregopher/mediocre-go-lib/mctx"
 	"github.com/mediocregopher/mediocre-go-lib/merr"
 )
@@ -34,7 +31,7 @@ import (
 func sortParams(params []Param) {
 	sort.Slice(params, func(i, j int) bool {
 		a, b := params[i], params[j]
-		aPath, bPath := mctx.Path(a.Context), mctx.Path(b.Context)
+		aPath, bPath := a.Component.Path(), b.Component.Path()
 		for {
 			switch {
 			case len(aPath) == 0 && len(bPath) == 0:
@@ -52,23 +49,23 @@ func sortParams(params []Param) {
 	})
 }
 
-// CollectParams gathers all Params by recursively retrieving them from this
-// Context and its children. Returned Params are sorted according to their Path
-// and Name.
-func CollectParams(ctx context.Context) []Param {
+// CollectParams gathers all Params by recursively retrieving them from the
+// given Component and its children. Returned Params are sorted according to
+// their Path and Name.
+func CollectParams(cmp *mcmp.Component) []Param {
 	var params []Param
 
-	var visit func(context.Context)
-	visit = func(ctx context.Context) {
-		for _, param := range getLocalParams(ctx) {
+	var visit func(*mcmp.Component)
+	visit = func(cmp *mcmp.Component) {
+		for _, param := range getLocalParams(cmp) {
 			params = append(params, param)
 		}
 
-		for _, childCtx := range mctx.Children(ctx) {
-			visit(childCtx)
+		for _, childCmp := range cmp.Children() {
+			visit(childCmp)
 		}
 	}
-	visit(ctx)
+	visit(cmp)
 
 	sortParams(params)
 	return params
@@ -86,34 +83,31 @@ func paramHash(path []string, name string) string {
 }
 
 // Populate uses the Source to populate the values of all Params which were
-// added to the given Context, and all of its children. Populate may be called
-// multiple times with the same Context, each time will only affect the values
+// added to the given Component, and all of its children. Populate may be called
+// multiple times with the same Component, each time will only affect the values
 // of the Params which were provided by the respective Source.
 //
-// Populating Params can affect the Context itself, for example in the case of
-// sub-commands. For this reason Populate will return a Context instance which
-// may have been affected by the Params (or, if not, will be the same one which
-// was passed in).
-//
 // Source may be nil to indicate that no configuration is provided. Only default
 // values will be used, and if any parameters are required this will error.
-func Populate(ctx context.Context, src Source) (context.Context, error) {
+//
+// Populating Params can affect the Component itself, for example in the case of
+// sub-commands.
+func Populate(cmp *mcmp.Component, src Source) error {
 	if src == nil {
 		src = ParamValues(nil)
 	}
-	ogCtx := ctx
 
-	ctx, pvs, err := src.Parse(ctx)
+	pvs, err := src.Parse(cmp)
 	if err != nil {
-		return ogCtx, err
+		return err
 	}
 
 	// map Params to their hash, so we can match them to their ParamValues.
 	// later. There should not be any duplicates here.
-	params := CollectParams(ctx)
+	params := CollectParams(cmp)
 	pM := map[string]Param{}
 	for _, p := range params {
-		path := mctx.Path(p.Context)
+		path := p.Component.Path()
 		hash := paramHash(path, p.Name)
 		if _, ok := pM[hash]; ok {
 			panic("duplicate Param: " + paramFullName(path, p.Name))
@@ -137,9 +131,9 @@ func Populate(ctx context.Context, src Source) (context.Context, error) {
 		if !p.Required {
 			continue
 		} else if _, ok := pvM[hash]; !ok {
-			ctx := mctx.Annotate(p.Context,
-				"param", paramFullName(mctx.Path(p.Context), p.Name))
-			return ogCtx, merr.New("required parameter is not set", ctx)
+			ctx := mctx.Annotate(p.Component.Annotated(),
+				"param", paramFullName(p.Component.Path(), p.Name))
+			return merr.New("required parameter is not set", ctx)
 		}
 	}
 
@@ -148,9 +142,9 @@ func Populate(ctx context.Context, src Source) (context.Context, error) {
 		// at this point, all ParamValues in pvM have a corresponding pM Param
 		p := pM[hash]
 		if err := json.Unmarshal(pv.Value, p.Into); err != nil {
-			return ogCtx, err
+			return err
 		}
 	}
 
-	return ctx, nil
+	return nil
 }
diff --git a/mcfg/mcfg_test.go b/mcfg/mcfg_test.go
index 583c756..bbc7470 100644
--- a/mcfg/mcfg_test.go
+++ b/mcfg/mcfg_test.go
@@ -1,45 +1,44 @@
 package mcfg
 
 import (
-	"context"
 	. "testing"
 
-	"github.com/mediocregopher/mediocre-go-lib/mctx"
+	"github.com/mediocregopher/mediocre-go-lib/mcmp"
 	"github.com/stretchr/testify/assert"
 )
 
 func TestPopulate(t *T) {
 	{
-		ctx := context.Background()
-		ctx, a := WithInt(ctx, "a", 0, "")
-		ctxChild := mctx.NewChild(ctx, "foo")
-		ctxChild, b := WithInt(ctxChild, "b", 0, "")
-		ctxChild, c := WithInt(ctxChild, "c", 0, "")
-		ctx = mctx.WithChild(ctx, ctxChild)
+		cmp := new(mcmp.Component)
+		a := Int(cmp, "a")
+		cmpFoo := cmp.Child("foo")
+		b := Int(cmpFoo, "b")
+		c := Int(cmpFoo, "c")
+		d := Int(cmp, "d", ParamDefault(4))
 
-		_, err := Populate(ctx, &SourceCLI{
+		err := Populate(cmp, &SourceCLI{
 			Args: []string{"--a=1", "--foo-b=2"},
 		})
 		assert.NoError(t, err)
 		assert.Equal(t, 1, *a)
 		assert.Equal(t, 2, *b)
 		assert.Equal(t, 0, *c)
+		assert.Equal(t, 4, *d)
 	}
 
 	{ // test that required params are enforced
-		ctx := context.Background()
-		ctx, a := WithInt(ctx, "a", 0, "")
-		ctxChild := mctx.NewChild(ctx, "foo")
-		ctxChild, b := WithInt(ctxChild, "b", 0, "")
-		ctxChild, c := WithRequiredInt(ctxChild, "c", "")
-		ctx = mctx.WithChild(ctx, ctxChild)
+		cmp := new(mcmp.Component)
+		a := Int(cmp, "a")
+		cmpFoo := cmp.Child("foo")
+		b := Int(cmpFoo, "b")
+		c := Int(cmpFoo, "c", ParamRequired())
 
-		_, err := Populate(ctx, &SourceCLI{
+		err := Populate(cmp, &SourceCLI{
 			Args: []string{"--a=1", "--foo-b=2"},
 		})
 		assert.Error(t, err)
 
-		_, err = Populate(ctx, &SourceCLI{
+		err = Populate(cmp, &SourceCLI{
 			Args: []string{"--a=1", "--foo-b=2", "--foo-c=3"},
 		})
 		assert.NoError(t, err)
diff --git a/mcfg/param.go b/mcfg/param.go
index 84c0708..26a405b 100644
--- a/mcfg/param.go
+++ b/mcfg/param.go
@@ -1,26 +1,25 @@
 package mcfg
 
 import (
-	"context"
 	"encoding/json"
 	"fmt"
+	"reflect"
 	"strings"
 
-	"github.com/mediocregopher/mediocre-go-lib/mctx"
+	"github.com/mediocregopher/mediocre-go-lib/mcmp"
 	"github.com/mediocregopher/mediocre-go-lib/mtime"
 )
 
 // Param is a configuration parameter which can be populated by Populate. The
-// Param will exist as part of a Context, relative to its path (see the mctx
-// package for more on Context path). For example, a Param with name "addr"
-// under a Context with path of []string{"foo","bar"} will be setable on the CLI
-// via "--foo-bar-addr". Other configuration Sources may treat the path/name
-// differently, however.
+// Param will exist as part of a Component. For example, a Param with name
+// "addr" under a Component with path of []string{"foo","bar"} will be setable
+// on the CLI via "--foo-bar-addr". Other configuration Sources may treat the
+// path/name differently, however.
 //
 // Param values are always unmarshaled as JSON values into the Into field of the
 // Param, regardless of the actual Source.
 type Param struct {
-	// How the parameter will be identified within a Context.
+	// How the parameter will be identified within a Component.
 	Name string
 
 	// A helpful description of how a parameter is expected to be used.
@@ -44,9 +43,59 @@ type Param struct {
 	// value of the parameter.
 	Into interface{}
 
-	// The Context this Param was added to. NOTE that this will be automatically
-	// filled in by WithParam when the Param is added to the Context.
-	Context context.Context
+	// The Component this Param was added to. NOTE that this will be
+	// automatically filled in by AddParam when the Param is added to the
+	// Component.
+	Component *mcmp.Component
+}
+
+// ParamOption is a modifier which can be passed into most Param-generating
+// functions (e.g. String, Int, etc...)
+type ParamOption func(*Param)
+
+// ParamRequired returns a ParamOption which ensures the parameter is required
+// to be set by some configuration source. The default value of the parameter
+// will be ignored.
+func ParamRequired() ParamOption {
+	return func(param *Param) {
+		param.Required = true
+	}
+}
+
+// ParamDefault returns a ParamOption which ensures the parameter uses the given
+// default value when no Sources set a value for it. If not given then mcfg will
+// use the zero value of the Param's type as the default value.
+//
+// If ParamRequired is given then this does nothing.
+func ParamDefault(value interface{}) ParamOption {
+	return func(param *Param) {
+		intoV := reflect.ValueOf(param.Into).Elem()
+		valueV := reflect.ValueOf(value)
+
+		intoType, valueType := intoV.Type(), valueV.Type()
+		if intoType != valueType {
+			panic(fmt.Sprintf("ParamDefault value is type %s, but should be %s", valueType, intoType))
+		} else if !intoV.CanSet() {
+			panic(fmt.Sprintf("Param.Into value %#v can't be set using reflection", param.Into))
+		}
+
+		intoV.Set(valueV)
+	}
+}
+
+// ParamUsage returns a ParamOption which sets the usage string on the Param.
+// This is used in some Sources, like SourceCLI, when displaying information
+// about available parameters.
+func ParamUsage(usage string) ParamOption {
+	// make all usages end with a period, because I say so
+	usage = strings.TrimSpace(usage)
+	if !strings.HasSuffix(usage, ".") {
+		usage += "."
+	}
+
+	return func(param *Param) {
+		param.Usage = usage
+	}
 }
 
 func paramFullName(path []string, name string) string {
@@ -67,31 +116,36 @@ func (p Param) fuzzyParse(v string) json.RawMessage {
 	return json.RawMessage(v)
 }
 
-type ctxKey string
+type cmpParamKey string
 
-func getParam(ctx context.Context, name string) (Param, bool) {
-	param, ok := mctx.LocalValue(ctx, ctxKey(name)).(Param)
+// used in tests
+func getParam(cmp *mcmp.Component, name string) (Param, bool) {
+	param, ok := cmp.Value(cmpParamKey(name)).(Param)
 	return param, ok
 }
 
-// WithParam returns a Context with the given Param added to it. It will panic
-// if a Param with the same Name already exists in the Context.
-func WithParam(ctx context.Context, param Param) context.Context {
+// AddParam adds the given Param to the given Component. It will panic if a
+// Param with the same Name already exists in the Component.
+func AddParam(cmp *mcmp.Component, param Param, opts ...ParamOption) {
 	param.Name = strings.ToLower(param.Name)
-	param.Context = ctx
+	param.Component = cmp
+	key := cmpParamKey(param.Name)
 
-	if _, ok := getParam(ctx, param.Name); ok {
-		path := mctx.Path(ctx)
-		panic(fmt.Sprintf("Context Path:%#v Name:%q already exists", path, param.Name))
+	if cmp.HasValue(key) {
+		path := cmp.Path()
+		panic(fmt.Sprintf("Component.Path:%#v Param.Name:%q already exists", path, param.Name))
 	}
 
-	return mctx.WithLocalValue(ctx, ctxKey(param.Name), param)
+	for _, opt := range opts {
+		opt(&param)
+	}
+	cmp.SetValue(key, param)
 }
 
-func getLocalParams(ctx context.Context) []Param {
-	localVals := mctx.LocalValues(ctx)
-	params := make([]Param, 0, len(localVals))
-	for _, val := range localVals {
+func getLocalParams(cmp *mcmp.Component) []Param {
+	values := cmp.Values()
+	params := make([]Param, 0, len(values))
+	for _, val := range values {
 		if param, ok := val.(Param); ok {
 			params = append(params, param)
 		}
@@ -99,131 +153,73 @@ func getLocalParams(ctx context.Context) []Param {
 	return params
 }
 
-// WithInt64 returns an *int64 which will be populated once Populate is run on
-// the returned Context.
-func WithInt64(ctx context.Context, name string, defaultVal int64, usage string) (context.Context, *int64) {
-	i := defaultVal
-	ctx = WithParam(ctx, Param{Name: name, Usage: usage, Into: &i})
-	return ctx, &i
-}
-
-// WithRequiredInt64 returns an *int64 which will be populated once Populate is
-// run on the returned Context, and which must be supplied by a configuration
-// Source.
-func WithRequiredInt64(ctx context.Context, name string, usage string) (context.Context, *int64) {
+// Int64 returns an *int64 which will be populated once Populate is run on the
+// Component.
+func Int64(cmp *mcmp.Component, name string, opts ...ParamOption) *int64 {
 	var i int64
-	ctx = WithParam(ctx, Param{Name: name, Required: true, Usage: usage, Into: &i})
-	return ctx, &i
+	AddParam(cmp, Param{Name: name, Into: &i}, opts...)
+	return &i
 }
 
-// WithInt returns an *int which will be populated once Populate is run on the
-// returned Context.
-func WithInt(ctx context.Context, name string, defaultVal int, usage string) (context.Context, *int) {
-	i := defaultVal
-	ctx = WithParam(ctx, Param{Name: name, Usage: usage, Into: &i})
-	return ctx, &i
-}
-
-// WithRequiredInt returns an *int which will be populated once Populate is run
-// on the returned Context, and which must be supplied by a configuration
-// Source.
-func WithRequiredInt(ctx context.Context, name string, usage string) (context.Context, *int) {
+// Int returns an *int which will be populated once Populate is run on the
+// Component.
+func Int(cmp *mcmp.Component, name string, opts ...ParamOption) *int {
 	var i int
-	ctx = WithParam(ctx, Param{Name: name, Required: true, Usage: usage, Into: &i})
-	return ctx, &i
+	AddParam(cmp, Param{Name: name, Into: &i}, opts...)
+	return &i
 }
 
-// WithFloat64 returns a *float64 which will be populated once Populate is run on
-// the returned Context.
-func WithFloat64(ctx context.Context, name string, defaultVal float64, usage string) (context.Context, *float64) {
-	f := defaultVal
-	ctx = WithParam(ctx, Param{Name: name, Usage: usage, Into: &f})
-	return ctx, &f
+// Float64 returns a *float64 which will be populated once Populate is run on
+// the Component
+func Float64(cmp *mcmp.Component, name string, opts ...ParamOption) *float64 {
+	var f float64
+	AddParam(cmp, Param{Name: name, Into: &f}, opts...)
+	return &f
 }
 
-// WithRequiredFloat64 returns a *float64 which will be populated once Populate
-// is run on the returned Context, and which must be supplied by a configuration
-// Source.
-func WithRequiredFloat64(ctx context.Context, name string, defaultVal float64, usage string) (context.Context, *float64) {
-	f := defaultVal
-	ctx = WithParam(ctx, Param{Name: name, Required: true, Usage: usage, Into: &f})
-	return ctx, &f
-}
-
-// WithString returns a *string which will be populated once Populate is run on
-// the returned Context.
-func WithString(ctx context.Context, name, defaultVal, usage string) (context.Context, *string) {
-	s := defaultVal
-	ctx = WithParam(ctx, Param{Name: name, Usage: usage, IsString: true, Into: &s})
-	return ctx, &s
-}
-
-// WithRequiredString returns a *string which will be populated once Populate is
-// run on the returned Context, and which must be supplied by a configuration
-// Source.
-func WithRequiredString(ctx context.Context, name, usage string) (context.Context, *string) {
+// String returns a *string which will be populated once Populate is run on
+// the Component.
+func String(cmp *mcmp.Component, name string, opts ...ParamOption) *string {
 	var s string
-	ctx = WithParam(ctx, Param{Name: name, Required: true, Usage: usage, IsString: true, Into: &s})
-	return ctx, &s
+	AddParam(cmp, Param{Name: name, IsString: true, Into: &s}, opts...)
+	return &s
 }
 
-// WithBool returns a *bool which will be populated once Populate is run on the
-// returned Context, and which defaults to false if unconfigured.
+// Bool returns a *bool which will be populated once Populate is run on the
+// Component, and which defaults to false if unconfigured.
 //
 // The default behavior of all Sources is that a boolean parameter will be set
 // to true unless the value is "", 0, or false. In the case of the CLI Source
 // the value will also be true when the parameter is used with no value at all,
 // as would be expected.
-func WithBool(ctx context.Context, name, usage string) (context.Context, *bool) {
+func Bool(cmp *mcmp.Component, name string, opts ...ParamOption) *bool {
 	var b bool
-	ctx = WithParam(ctx, Param{Name: name, Usage: usage, IsBool: true, Into: &b})
-	return ctx, &b
+	AddParam(cmp, Param{Name: name, IsBool: true, Into: &b}, opts...)
+	return &b
 }
 
-// WithTS returns an *mtime.TS which will be populated once Populate is run on
-// the returned Context.
-func WithTS(ctx context.Context, name string, defaultVal mtime.TS, usage string) (context.Context, *mtime.TS) {
-	t := defaultVal
-	ctx = WithParam(ctx, Param{Name: name, Usage: usage, Into: &t})
-	return ctx, &t
-}
-
-// WithRequiredTS returns an *mtime.TS which will be populated once Populate is
-// run on the returned Context, and which must be supplied by a configuration
-// Source.
-func WithRequiredTS(ctx context.Context, name, usage string) (context.Context, *mtime.TS) {
+// TS returns an *mtime.TS which will be populated once Populate is run on
+// the Component.
+func TS(cmp *mcmp.Component, name string, opts ...ParamOption) *mtime.TS {
 	var t mtime.TS
-	ctx = WithParam(ctx, Param{Name: name, Required: true, Usage: usage, Into: &t})
-	return ctx, &t
+	AddParam(cmp, Param{Name: name, Into: &t}, opts...)
+	return &t
 }
 
-// WithDuration returns an *mtime.Duration which will be populated once Populate
-// is run on the returned Context.
-func WithDuration(ctx context.Context, name string, defaultVal mtime.Duration, usage string) (context.Context, *mtime.Duration) {
-	d := defaultVal
-	ctx = WithParam(ctx, Param{Name: name, Usage: usage, IsString: true, Into: &d})
-	return ctx, &d
-}
-
-// WithRequiredDuration returns an *mtime.Duration which will be populated once
-// Populate is run on the returned Context, and which must be supplied by a
-// configuration Source.
-func WithRequiredDuration(ctx context.Context, name string, defaultVal mtime.Duration, usage string) (context.Context, *mtime.Duration) {
+// Duration returns an *mtime.Duration which will be populated once Populate
+// is run on the Component.
+func Duration(cmp *mcmp.Component, name string, opts ...ParamOption) *mtime.Duration {
 	var d mtime.Duration
-	ctx = WithParam(ctx, Param{Name: name, Required: true, Usage: usage, IsString: true, Into: &d})
-	return ctx, &d
+	AddParam(cmp, Param{Name: name, IsString: true, Into: &d}, opts...)
+	return &d
 }
 
-// WithJSON reads the parameter value as a JSON value and unmarshals it into the
-// given interface{} (which should be a pointer). The receiver (into) is also
-// used to determine the default value.
-func WithJSON(ctx context.Context, name string, into interface{}, usage string) context.Context {
-	return WithParam(ctx, Param{Name: name, Usage: usage, Into: into})
-}
-
-// WithRequiredJSON reads the parameter value as a JSON value and unmarshals it
-// into the given interface{} (which should be a pointer). The value must be
-// supplied by a configuration Source.
-func WithRequiredJSON(ctx context.Context, name string, into interface{}, usage string) context.Context {
-	return WithParam(ctx, Param{Name: name, Required: true, Usage: usage, Into: into})
+// JSON reads the parameter value as a JSON value and unmarshals it into the
+// given interface{} (which should be a pointer) once Populate is run on the
+// Component.
+//
+// The receiver (into) is also used to determine the default value. ParamDefault
+// should not be used as one of the opts.
+func JSON(cmp *mcmp.Component, name string, into interface{}, opts ...ParamOption) {
+	AddParam(cmp, Param{Name: name, Into: into}, opts...)
 }
diff --git a/mcfg/source.go b/mcfg/source.go
index 92642cf..48dca2c 100644
--- a/mcfg/source.go
+++ b/mcfg/source.go
@@ -1,8 +1,9 @@
 package mcfg
 
 import (
-	"context"
 	"encoding/json"
+
+	"github.com/mediocregopher/mediocre-go-lib/mcmp"
 )
 
 // ParamValue describes a value for a parameter which has been parsed by a
@@ -14,31 +15,32 @@ type ParamValue struct {
 }
 
 // Source parses ParamValues out of a particular configuration source, given the
-// Context which the Params were added to (via WithInt, WithString, etc...).
+// Component which the Params were added to (via WithInt, WithString, etc...).
 // CollectParams can be used to retrieve these Params.
 //
-// It's possible for Parsing to affect the Context itself, for example in the
-// case of sub-commands. For this reason Parse can return a Context, which will
-// get used for subsequent Parse commands inside Populate.
+// It's possible for Parsing to affect the Component itself, for example in the
+// case of sub-commands.
 //
 // Source should not return ParamValues which were not explicitly set to a value
 // by the configuration source.
 //
 // The returned []ParamValue may contain duplicates of the same Param's value.
-// in which case the later value takes precedence. It may also contain
+// in which case the latter value takes precedence. It may also contain
 // ParamValues which do not correspond to any of the passed in Params. These
 // will be ignored in Populate.
 type Source interface {
-	Parse(context.Context) (context.Context, []ParamValue, error)
+	Parse(*mcmp.Component) ([]ParamValue, error)
 }
 
 // ParamValues is simply a slice of ParamValue elements, which implements Parse
 // by always returning itself as-is.
 type ParamValues []ParamValue
 
+var _ Source = ParamValues{}
+
 // Parse implements the method for the Source interface.
-func (pvs ParamValues) Parse(ctx context.Context) (context.Context, []ParamValue, error) {
-	return ctx, pvs, nil
+func (pvs ParamValues) Parse(*mcmp.Component) ([]ParamValue, error) {
+	return pvs, nil
 }
 
 // Sources combines together multiple Source instances into one. It will call
@@ -46,16 +48,18 @@ func (pvs ParamValues) Parse(ctx context.Context) (context.Context, []ParamValue
 // over previous ones.
 type Sources []Source
 
+var _ Source = Sources{}
+
 // Parse implements the method for the Source interface.
-func (ss Sources) Parse(ctx context.Context) (context.Context, []ParamValue, error) {
+func (ss Sources) Parse(cmp *mcmp.Component) ([]ParamValue, error) {
 	var pvs []ParamValue
 	for _, s := range ss {
 		var innerPVs []ParamValue
 		var err error
-		if ctx, innerPVs, err = s.Parse(ctx); err != nil {
-			return nil, nil, err
+		if innerPVs, err = s.Parse(cmp); err != nil {
+			return nil, err
 		}
 		pvs = append(pvs, innerPVs...)
 	}
-	return ctx, pvs, nil
+	return pvs, nil
 }
diff --git a/mcfg/source_test.go b/mcfg/source_test.go
index e72483b..8937d68 100644
--- a/mcfg/source_test.go
+++ b/mcfg/source_test.go
@@ -1,13 +1,12 @@
 package mcfg
 
 import (
-	"context"
 	"encoding/json"
 	"fmt"
 	. "testing"
 	"time"
 
-	"github.com/mediocregopher/mediocre-go-lib/mctx"
+	"github.com/mediocregopher/mediocre-go-lib/mcmp"
 	"github.com/mediocregopher/mediocre-go-lib/mrand"
 	"github.com/mediocregopher/mediocre-go-lib/mtest/massert"
 )
@@ -17,10 +16,9 @@ import (
 // all the code they share
 
 type srcCommonState struct {
-	// availCtxs get updated in place as the run goes on, and mkRoot is used to
-	// create the latest version of the root context based on them
-	availCtxs []*context.Context
-	mkRoot    func() context.Context
+	// availCmps get updated in place as the run goes on, it's easier to keep
+	// track of them this way than by traversing the hierarchy.
+	availCmps []*mcmp.Component
 
 	expPVs []ParamValue
 	// each specific test should wrap this to add the Source itself
@@ -29,31 +27,21 @@ type srcCommonState struct {
 func newSrcCommonState() srcCommonState {
 	var scs srcCommonState
 	{
-		root := context.Background()
-		a := mctx.NewChild(root, "a")
-		b := mctx.NewChild(root, "b")
-		c := mctx.NewChild(root, "c")
-		ab := mctx.NewChild(a, "b")
-		bc := mctx.NewChild(b, "c")
-		abc := mctx.NewChild(ab, "c")
-		scs.availCtxs = []*context.Context{&root, &a, &b, &c, &ab, &bc, &abc}
-		scs.mkRoot = func() context.Context {
-			ab := mctx.WithChild(ab, abc)
-			a := mctx.WithChild(a, ab)
-			b := mctx.WithChild(b, bc)
-			root := mctx.WithChild(root, a)
-			root = mctx.WithChild(root, b)
-			root = mctx.WithChild(root, c)
-			return root
-		}
+		root := new(mcmp.Component)
+		a := root.Child("a")
+		b := root.Child("b")
+		c := root.Child("c")
+		ab := a.Child("b")
+		bc := b.Child("c")
+		abc := ab.Child("c")
+		scs.availCmps = []*mcmp.Component{root, a, b, c, ab, bc, abc}
 	}
 	return scs
 }
 
 type srcCommonParams struct {
 	name        string
-	availCtxI   int // not technically needed, but makes finding the ctx easier
-	path        []string
+	cmp         *mcmp.Component
 	isBool      bool
 	nonBoolType string // "int", "str", "duration", "json"
 	unset       bool
@@ -68,8 +56,8 @@ func (scs srcCommonState) next() srcCommonParams {
 		p.name = mrand.Hex(8)
 	}
 
-	p.availCtxI = mrand.Intn(len(scs.availCtxs))
-	p.path = mctx.Path(*scs.availCtxs[p.availCtxI])
+	availCmpI := mrand.Intn(len(scs.availCmps))
+	p.cmp = scs.availCmps[availCmpI]
 
 	p.isBool = mrand.Intn(8) == 0
 	if !p.isBool {
@@ -105,22 +93,21 @@ func (scs srcCommonState) next() srcCommonParams {
 	return p
 }
 
-// adds the new param to the ctx, and if the param is expected to be set in
+// adds the new param to the cmp, and if the param is expected to be set in
 // the Source adds it to the expected ParamValues as well
-func (scs srcCommonState) applyCtxAndPV(p srcCommonParams) srcCommonState {
-	thisCtx := scs.availCtxs[p.availCtxI]
-	ctxP := Param{
+func (scs srcCommonState) applyCmpAndPV(p srcCommonParams) srcCommonState {
+	param := Param{
 		Name:     p.name,
 		IsString: p.nonBoolType == "str" || p.nonBoolType == "duration",
 		IsBool:   p.isBool,
 		// the Sources don't actually care about the other fields of Param,
 		// those are only used by Populate once it has all ParamValues together
 	}
-	*thisCtx = WithParam(*thisCtx, ctxP)
-	ctxP, _ = getParam(*thisCtx, ctxP.Name) // get it back out to get any added fields
+	AddParam(p.cmp, param)
+	param, _ = getParam(p.cmp, param.Name) // get it back out to get any added fields
 
 	if !p.unset {
-		pv := ParamValue{Name: ctxP.Name, Path: mctx.Path(ctxP.Context)}
+		pv := ParamValue{Name: param.Name, Path: p.cmp.Path()}
 		if p.isBool {
 			pv.Value = json.RawMessage("true")
 		} else {
@@ -142,8 +129,7 @@ func (scs srcCommonState) applyCtxAndPV(p srcCommonParams) srcCommonState {
 // given a Source asserts that it's Parse method returns the expected
 // ParamValues
 func (scs srcCommonState) assert(s Source) error {
-	root := scs.mkRoot()
-	_, gotPVs, err := s.Parse(root)
+	gotPVs, err := s.Parse(scs.availCmps[0]) // Parse(root)
 	if err != nil {
 		return err
 	}
@@ -154,12 +140,12 @@ func (scs srcCommonState) assert(s Source) error {
 }
 
 func TestSources(t *T) {
-	ctx := context.Background()
-	ctx, a := WithRequiredInt(ctx, "a", "")
-	ctx, b := WithRequiredInt(ctx, "b", "")
-	ctx, c := WithRequiredInt(ctx, "c", "")
+	cmp := new(mcmp.Component)
+	a := Int(cmp, "a", ParamRequired())
+	b := Int(cmp, "b", ParamRequired())
+	c := Int(cmp, "c", ParamRequired())
 
-	_, err := Populate(ctx, Sources{
+	err := Populate(cmp, Sources{
 		&SourceCLI{Args: []string{"--a=1", "--b=666"}},
 		&SourceEnv{Env: []string{"B=2", "C=3"}},
 	})
@@ -172,14 +158,13 @@ func TestSources(t *T) {
 }
 
 func TestSourceParamValues(t *T) {
-	ctx := context.Background()
-	ctx, a := WithRequiredInt(ctx, "a", "")
-	foo := mctx.NewChild(ctx, "foo")
-	foo, b := WithRequiredString(foo, "b", "")
-	foo, c := WithBool(foo, "c", "")
-	ctx = mctx.WithChild(ctx, foo)
+	cmp := new(mcmp.Component)
+	a := Int(cmp, "a", ParamRequired())
+	cmpFoo := cmp.Child("foo")
+	b := String(cmpFoo, "b", ParamRequired())
+	c := Bool(cmpFoo, "c")
 
-	_, err := Populate(ctx, ParamValues{
+	err := Populate(cmp, ParamValues{
 		{Name: "a", Value: json.RawMessage(`4`)},
 		{Path: []string{"foo"}, Name: "b", Value: json.RawMessage(`"bbb"`)},
 		{Path: []string{"foo"}, Name: "c", Value: json.RawMessage("true")},