mcfg: refactor to remove Child and Hook stuff, and use mctx instead

mcfg/cli.go

@@ -11,11 +11,13 @@ import (
 
 // SourceCLI is a Source which will parse configuration from the CLI.
 //
-// Possible CLI options are generated by joining the Path to a Param, and its
+// Possible CLI options are generated by joining a Param's Path and Name with
-// name, with dashes. For example:
+// dashes. For example:
 //
-//	cfg := mcfg.New().Child("foo").Child("bar")
+//	ctx := mctx.New()
-//	addr := cfg.ParamString("addr", "", "Some address")
+//	ctx = mctx.ChildOf(ctx, "foo")
+//	ctx = mctx.ChildOf(ctx, "bar")
+//	addr := mcfg.String(ctx, "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
@@ -41,13 +43,13 @@ const (
 )
 
 // Parse implements the method for the Source interface
-func (cli SourceCLI) Parse(cfg *Cfg) ([]ParamValue, error) {
+func (cli SourceCLI) Parse(params []Param) ([]ParamValue, error) {
 	args := cli.Args
 	if cli.Args == nil {
 		args = os.Args[1:]
 	}
 
-	pM, err := cli.cliParams(cfg)
+	pM, err := cli.cliParams(params)
 	if err != nil {
 		return nil, err
 	}
@@ -117,9 +119,9 @@ func (cli SourceCLI) Parse(cfg *Cfg) ([]ParamValue, error) {
 	return pvs, nil
 }
 
-func (cli SourceCLI) cliParams(cfg *Cfg) (map[string]Param, error) {
+func (cli SourceCLI) cliParams(params []Param) (map[string]Param, error) {
 	m := map[string]Param{}
-	for _, p := range cfg.allParams() {
+	for _, p := range params {
 		key := strings.Join(append(p.Path, p.Name), cliKeyJoin)
 		m[cliKeyPrefix+key] = p
 	}

mcfg/cli_test.go

@@ -6,6 +6,7 @@ import (
 	. "testing"
 	"time"
 
+	"github.com/mediocregopher/mediocre-go-lib/mctx"
 	"github.com/mediocregopher/mediocre-go-lib/mrand"
 	"github.com/mediocregopher/mediocre-go-lib/mtest/mchk"
 	"github.com/stretchr/testify/assert"
@@ -13,15 +14,15 @@ import (
 )
 
 func TestSourceCLIHelp(t *T) {
-	cfg := New()
+	ctx := mctx.New()
-	cfg.ParamInt("foo", 5, "Test int param")
+	Int(ctx, "foo", 5, "Test int param")
-	cfg.ParamBool("bar", "Test bool param")
+	Bool(ctx, "bar", "Test bool param")
-	cfg.ParamString("baz", "baz", "Test string param")
+	String(ctx, "baz", "baz", "Test string param")
-	cfg.ParamString("baz2", "", "")
+	String(ctx, "baz2", "", "")
 	src := SourceCLI{}
 
 	buf := new(bytes.Buffer)
-	pM, err := src.cliParams(cfg)
+	pM, err := src.cliParams(collectParams(ctx))
 	require.NoError(t, err)
 	SourceCLI{}.printHelp(buf, pM)
 
@@ -71,7 +72,7 @@ func TestSourceCLI(t *T) {
 			s := ss.(state)
 			p := a.Params.(params)
 
-			s.srcCommonState = s.srcCommonState.applyCfgAndPV(p.srcCommonParams)
+			s.srcCommonState = s.srcCommonState.applyCtxAndPV(p.srcCommonParams)
 			if !p.unset {
 				arg := cliKeyPrefix
 				if len(p.path) > 0 {

mcfg/env.go

@@ -13,12 +13,15 @@ import (
 // underscores and making all characters uppercase, as well as changing all
 // dashes to underscores.
 //
-//	cfg := mcfg.New().Child("foo").Child("bar")
+//	ctx := mctx.New()
-//	addr := cfg.ParamString("srv-addr", "", "Some address")
+//	ctx = mctx.ChildOf(ctx, "foo")
+//	ctx = mctx.ChildOf(ctx, "bar")
+//	addr := mcfg.String(ctx, "srv-addr", "", "Some address")
 //	// the Env option to fill addr will be "FOO_BAR_SRV_ADDR"
 //
 type SourceEnv struct {
-	Env []string // in the format key=value
+	// In the format key=value. Defaults to os.Environ() if nil.
+	Env []string
 
 	// If set then all expected Env options must be prefixed with this string,
 	// which will be uppercased and have dashes replaced with underscores like
@@ -37,14 +40,14 @@ func (env SourceEnv) expectedName(path []string, name string) string {
 }
 
 // Parse implements the method for the Source interface
-func (env SourceEnv) Parse(cfg *Cfg) ([]ParamValue, error) {
+func (env SourceEnv) Parse(params []Param) ([]ParamValue, error) {
 	kvs := env.Env
 	if kvs == nil {
 		kvs = os.Environ()
 	}
 
 	pM := map[string]Param{}
-	for _, p := range cfg.allParams() {
+	for _, p := range params {
 		name := env.expectedName(p.Path, p.Name)
 		pM[name] = p
 	}

mcfg/env_test.go

@@ -34,7 +34,7 @@ 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.applyCfgAndPV(p.srcCommonParams)
+			s.srcCommonState = s.srcCommonState.applyCtxAndPV(p.srcCommonParams)
 			if !p.unset {
 				kv := strings.Join(append(p.path, p.name), "_")
 				kv = strings.Replace(kv, "-", "_", -1)

mcfg/mcfg.go

@@ -3,133 +3,80 @@
 package mcfg
 
 import (
-	"context"
 	"encoding/json"
 	"fmt"
-	"strings"
+	"sort"
+
+	"github.com/mediocregopher/mediocre-go-lib/mctx"
 )
 
 // TODO Sources:
-// - Env file
 // - JSON file
 // - YAML file
 
-// Hook describes a function which can have other Hook functions appended to it
+type ctxCfg struct {
-// via the Then method. A Hook is expected to return context.Canceled on context
+	path   []string
-// cancellation.
+	params map[string]Param
-type Hook func(context.Context) error
-
-// Nop returns a Hook which does nothing
-func Nop() Hook {
-	return func(context.Context) error { return nil }
 }
 
-// Then modifies the called upon Hook such that it will first perform whatever
+type ctxKey int
-// it's original functionality was, and then if that doesn't return an error it
+
-// will subsequently perform the given Hook.
+func get(ctx mctx.Context) *ctxCfg {
-func (h *Hook) Then(h2 Hook) {
+	return mctx.GetSetMutableValue(ctx, true, ctxKey(0),
-	oldh := *h
+		func(interface{}) interface{} {
-	*h = func(ctx context.Context) error {
+			return &ctxCfg{
-		if err := oldh(ctx); err != nil {
+				path:   mctx.Path(ctx),
-			return err
+				params: map[string]Param{},
-		} else if err := ctx.Err(); err != nil {
-			// in case the previous hook doesn't respect the context
-			return err
-		}
-		return h2(ctx)
 			}
+		},
+	).(*ctxCfg)
 }
 
-// Also modifies the called upon Hook such that it will perform the original
+func sortParams(params []Param) {
-// functionality at the same time as the given Hook, wait for both to complete,
+	sort.Slice(params, func(i, j int) bool {
-// and return an error if there is one.
+		a, b := params[i], params[j]
-func (h *Hook) Also(h2 Hook) {
+		aPath, bPath := a.Path, b.Path
-	oldh := *h
+		for {
-	*h = func(ctx context.Context) error {
+			switch {
-		errCh := make(chan error, 1)
+			case len(aPath) == 0 && len(bPath) == 0:
-		go func() {
+				return a.Name < b.Name
-			errCh <- oldh(ctx)
+			case len(aPath) == 0 && len(bPath) > 0:
-		}()
+				return false
-		err := h2(ctx) // don't immediately return this, wait for h2 or ctx
+			case len(aPath) > 0 && len(bPath) == 0:
-		if err := ctx.Err(); err != nil {
+				return true
-			// in case the previous hook doesn't respect the context
+			case aPath[0] != bPath[0]:
-			return err
+				return aPath[0] < bPath[0]
-		} else if err := <-errCh; err != nil {
+			default:
-			return err
+				aPath, bPath = aPath[1:], bPath[1:]
-		}
-		return err
 			}
 		}
-
+	})
-// Cfg describes a set of configuration parameters and run-time behaviors.
-// Parameters are defined using the Param* methods, and run-time behaviors by
-// the Hook fields on this struct.
-//
-// Each Cfg can have child Cfg's spawned off of it using the Child method, which
-// allows for namespacing related params/behaviors into heirarchies.
-type Cfg struct {
-	// Read-only. The set of names passed into Child methods used to generate
-	// this Cfg and all of its parents. Path will be nil if this Cfg was created
-	// with New and not a Child call.
-	//
-	// Examples:
-	// New().Path                           is nil
-	// New().Child("foo").Path              is []string{"foo"}
-	// New().Child("foo").Child("bar").Path is []string{"foo", "bar"}
-	Path []string
-
-	// Read-only. The set of children spawned off of this Cfg via the Child
-	// method, keyed by the children's names.
-	Children map[string]*Cfg
-
-	// Read-only. The set of Params which have been added to the Cfg instance
-	// via its Add method.
-	Params map[string]Param
-
-	// Start hook is performed after configuration variables have been parsed
-	// and populated. All Start hooks are expected to run in a finite amount of
-	// time, any long running processes spun off from them should do so in a
-	// separate go-routine
-	Start Hook
-
-	// Stop hook is performed on interrupt signal, and should stop all
-	// go-routines and close all resource handlers created during Start
-	Stop Hook
 }
 
-// New initializes and returns an empty Cfg with default values filled in
+// returns all Params gathered by recursively retrieving them from this Context
-func New() *Cfg {
+// and its children. Returned Params are sorted according to their Path and
-	return &Cfg{
+// Name.
-		Children: map[string]*Cfg{},
+func collectParams(ctx mctx.Context) []Param {
-		Params:   map[string]Param{},
+	var params []Param
-		Start:    Nop(),
+
-		Stop:     Nop(),
+	var visit func(mctx.Context)
-	}
+	visit = func(ctx mctx.Context) {
+		for _, param := range get(ctx).params {
+			params = append(params, param)
 		}
 
-// IsRoot returns true if this is the root instance of a Cfg (i.e. the one
+		for _, childCtx := range mctx.Children(ctx) {
-// returned by New)
+			visit(childCtx)
-func (c *Cfg) IsRoot() bool {
+		}
-	return len(c.Path) == 0
+	}
+	visit(ctx)
+
+	sortParams(params)
+	return params
 }
 
-// Name returns the name given to this instance when it was created via Child.
+func populate(params []Param, src Source) error {
-// if this instance was created via New (i.e. it is the root instance) then
+	pvs, err := src.Parse(params)
-// empty string is returned.
-func (c *Cfg) Name() string {
-	if c.IsRoot() {
-		return ""
-	}
-	return c.Path[len(c.Path)-1]
-}
-
-// FullName returns a string representing the full path of the instance.
-func (c *Cfg) FullName() string {
-	return "/" + strings.Join(c.Path, "/")
-}
-
-func (c *Cfg) populateParams(src Source) error {
-	pvs, err := src.Parse(c)
 	if err != nil {
 		return err
 	}
@@ -142,11 +89,11 @@ func (c *Cfg) populateParams(src Source) error {
 	}
 
 	// check for required params
-	for _, p := range c.allParams() {
+	for _, param := range params {
-		if !p.Required {
+		if !param.Required {
 			continue
-		} else if _, ok := pvM[p.hash()]; !ok {
+		} else if _, ok := pvM[param.hash()]; !ok {
-			return fmt.Errorf("param %q is required", p.fullName())
+			return fmt.Errorf("param %q is required", param.fullName())
 		}
 	}
 
@@ -155,57 +102,12 @@ func (c *Cfg) populateParams(src Source) error {
 			return err
 		}
 	}
+
 	return nil
 }
 
-func (c *Cfg) runPreBlock(ctx context.Context, src Source) error {
+// Populate uses the Source to populate the values of all Params which were
-	if err := c.populateParams(src); err != nil {
+// added to the given mctx.Context, and all of its children.
-		return err
+func Populate(ctx mctx.Context, src Source) error {
-	}
+	return populate(collectParams(ctx), src)
-
-	return c.Start(ctx)
-}
-
-// StartRun blocks while performing all steps of a Cfg run. The steps, in order,
-// are:
-// * Populate all configuration parameters
-// * Perform Start hooks
-//
-// If any step returns an error then everything returns that error immediately.
-func (c *Cfg) StartRun(ctx context.Context, src Source) error {
-	return c.runPreBlock(ctx, src)
-}
-
-// StartTestRun is like StartRun, except it's intended to only be used during
-// tests to initialize other entities which are going to actually be tested. It
-// assumes all default configuration param values, and will return after the
-// Start hook has completed. It will panic on any errors.
-func (c *Cfg) StartTestRun() {
-	if err := c.runPreBlock(context.Background(), nil); err != nil {
-		panic(err)
-	}
-}
-
-// StopRun blocks while calling the Stop hook of the Cfg, returning any error
-// that it does.
-func (c *Cfg) StopRun(ctx context.Context) error {
-	return c.Stop(ctx)
-}
-
-// Child returns a sub-Cfg of the callee with the given name. The name will be
-// prepended to all configuration options created in the returned sub-Cfg, and
-// must not be empty.
-func (c *Cfg) Child(name string) *Cfg {
-	name = strings.ToLower(name)
-	if _, ok := c.Children[name]; ok {
-		panic(fmt.Sprintf("child Cfg named %q already exists", name))
-	}
-	c2 := New()
-	c2.Path = make([]string, 0, len(c.Path)+1)
-	c2.Path = append(c2.Path, c.Path...)
-	c2.Path = append(c2.Path, name)
-	c.Children[name] = c2
-	c.Start.Then(func(ctx context.Context) error { return c2.Start(ctx) })
-	c.Stop.Then(func(ctx context.Context) error { return c2.Stop(ctx) })
-	return c2
 }

mcfg/mcfg_test.go

@@ -1,96 +1,21 @@
 package mcfg
 
 import (
-	"context"
 	. "testing"
-	"time"
 
+	"github.com/mediocregopher/mediocre-go-lib/mctx"
 	"github.com/stretchr/testify/assert"
 )
 
-func TestHook(t *T) {
+func TestPopulate(t *T) {
-	{ // test Then
-		aCh := make(chan bool)
-		bCh := make(chan bool)
-		h := Nop()
-		h.Then(func(context.Context) error {
-			aCh <- true
-			<-aCh
-			return nil
-		})
-		h.Then(func(context.Context) error {
-			bCh <- true
-			<-bCh
-			return nil
-		})
-		errCh := make(chan error)
-		go func() {
-			errCh <- h(context.Background())
-		}()
-
-		assert.True(t, <-aCh)
-		// make sure bCh isn't being written to till aCh is closed
-		select {
-		case <-bCh:
-			assert.Fail(t, "bCh shouldn't be written to yet")
-		case <-time.After(250 * time.Millisecond):
-			close(aCh)
-		}
-		assert.True(t, <-bCh)
-		// make sure errCh isn't being written to till bCh is closed
-		select {
-		case <-errCh:
-			assert.Fail(t, "errCh shouldn't be written to yet")
-		case <-time.After(250 * time.Millisecond):
-			close(bCh)
-		}
-		assert.Nil(t, <-errCh)
-	}
-
-	{ // test Also
-		aCh := make(chan bool)
-		bCh := make(chan bool)
-		h := Nop()
-		h.Also(func(context.Context) error {
-			aCh <- true
-			<-aCh
-			return nil
-		})
-		h.Also(func(context.Context) error {
-			bCh <- true
-			<-bCh
-			return nil
-		})
-		errCh := make(chan error)
-		go func() {
-			errCh <- h(context.Background())
-		}()
-
-		// both channels should get written to, then closed, then errCh should
-		// get written to
-		assert.True(t, <-aCh)
-		assert.True(t, <-bCh)
-		// make sure errCh isn't being written to till both channels are written
-		select {
-		case <-errCh:
-			assert.Fail(t, "errCh shouldn't be written to yet")
-		case <-time.After(250 * time.Millisecond):
-			close(aCh)
-			close(bCh)
-		}
-		assert.Nil(t, <-errCh)
-	}
-}
-
-func TestPopulateParams(t *T) {
 	{
-		cfg := New()
+		ctx := mctx.New()
-		a := cfg.ParamInt("a", 0, "")
+		a := Int(ctx, "a", 0, "")
-		cfgChild := cfg.Child("foo")
+		ctxChild := mctx.ChildOf(ctx, "foo")
-		b := cfgChild.ParamInt("b", 0, "")
+		b := Int(ctxChild, "b", 0, "")
-		c := cfgChild.ParamInt("c", 0, "")
+		c := Int(ctxChild, "c", 0, "")
 
-		err := cfg.populateParams(SourceCLI{
+		err := Populate(ctx, SourceCLI{
 			Args: []string{"--a=1", "--foo-b=2"},
 		})
 		assert.NoError(t, err)
@@ -100,18 +25,18 @@ func TestPopulateParams(t *T) {
 	}
 
 	{ // test that required params are enforced
-		cfg := New()
+		ctx := mctx.New()
-		a := cfg.ParamInt("a", 0, "")
+		a := Int(ctx, "a", 0, "")
-		cfgChild := cfg.Child("foo")
+		ctxChild := mctx.ChildOf(ctx, "foo")
-		b := cfgChild.ParamInt("b", 0, "")
+		b := Int(ctxChild, "b", 0, "")
-		c := cfgChild.ParamRequiredInt("c", "")
+		c := RequiredInt(ctxChild, "c", "")
 
-		err := cfg.populateParams(SourceCLI{
+		err := Populate(ctx, SourceCLI{
 			Args: []string{"--a=1", "--foo-b=2"},
 		})
 		assert.Error(t, err)
 
-		err = cfg.populateParams(SourceCLI{
+		err = Populate(ctx, SourceCLI{
 			Args: []string{"--a=1", "--foo-b=2", "--foo-c=3"},
 		})
 		assert.NoError(t, err)
@@ -120,25 +45,3 @@ func TestPopulateParams(t *T) {
 		assert.Equal(t, 3, *c)
 	}
 }
-
-func TestChild(t *T) {
-	cfg := New()
-	assert.True(t, cfg.IsRoot())
-	assert.Equal(t, "", cfg.Name())
-	assert.Equal(t, "/", cfg.FullName())
-
-	foo := cfg.Child("foo")
-	assert.False(t, foo.IsRoot())
-	assert.Equal(t, "foo", foo.Name())
-	assert.Equal(t, "/foo", foo.FullName())
-
-	bar := cfg.Child("bar")
-	assert.False(t, bar.IsRoot())
-	assert.Equal(t, "bar", bar.Name())
-	assert.Equal(t, "/bar", bar.FullName())
-
-	foo2 := foo.Child("foo2")
-	assert.False(t, foo2.IsRoot())
-	assert.Equal(t, "foo2", foo2.Name())
-	assert.Equal(t, "/foo/foo2", foo2.FullName())
-}

mcfg/param.go

@@ -7,23 +7,28 @@ import (
 	"fmt"
 	"strings"
 
+	"github.com/mediocregopher/mediocre-go-lib/mctx"
 	"github.com/mediocregopher/mediocre-go-lib/mtime"
 )
 
-// Param is a configuration parameter which can be added to a Cfg. The Param
+// Param is a configuration parameter which can be populated by Populate. The
-// will exist relative to a Cfg's Path. For example, a Param with name "addr"
+// Param will exist as part of an mctx.Context, relative to its Path. For
-// under a Cfg with Path of []string{"foo","bar"} will be setabble on the CLI
+// example, a Param with name "addr" under an mctx.Context with Path of
-// via "--foo-bar-addr". Other configuration Sources may treat the path/name
+// []string{"foo","bar"} will be setabble on the CLI via "--foo-bar-addr". Other
-// differently, however.
+// 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 Cfg instance
+	// How the parameter will be identified within an mctx.Context.
 	Name string
-	// A helpful description of how a parameter is expected to be used
+
+	// A helpful description of how a parameter is expected to be used.
 	Usage string
 
 	// If the parameter's value is expected to be read as a go string. This is
-	// used for configuration sources like CLI which will automatically escape
+	// used for configuration sources like CLI which will automatically add
-	// the parameter's value with double-quotes
+	// double-quotes around the value if they aren't already there.
 	IsString bool
 
 	// If the parameter's value is expected to be a boolean. This is used for
@@ -31,8 +36,7 @@ type Param struct {
 	// differently.
 	IsBool bool
 
-	// If true then the parameter _must_ be set by at least one configuration
+	// If true then the parameter _must_ be set by at least one Source.
-	// source
 	Required bool
 
 	// The pointer/interface into which the configuration value will be
@@ -74,111 +78,118 @@ func (p Param) hash() string {
 	return p.fullName() + "/" + hStr
 }
 
-// ParamAdd adds the given Param to the Cfg. It will panic if a Param of the
+// MustAdd adds the given Param to the mctx.Context. It will panic if a Param of
-// same Name already exists in the Cfg.
+// the same Name already exists in the mctx.Context.
-func (c *Cfg) ParamAdd(p Param) {
+func MustAdd(ctx mctx.Context, param Param) {
-	p.Name = strings.ToLower(p.Name)
+	param.Name = strings.ToLower(param.Name)
-	if _, ok := c.Params[p.Name]; ok {
+	param.Path = mctx.Path(ctx)
-		panic(fmt.Sprintf("Cfg.Path:%#v name:%q already exists", c.Path, p.Name))
+
+	cfg := get(ctx)
+	if _, ok := cfg.params[param.Name]; ok {
+		panic(fmt.Sprintf("Context Path:%#v Name:%q already exists", param.Path, param.Name))
 	}
-	p.Path = c.Path
+	cfg.params[param.Name] = param
-	c.Params[p.Name] = p
 }
 
-func (c *Cfg) allParams() []Param {
+// Int64 returns an *int64 which will be populated once Populate is run.
-	params := make([]Param, 0, len(c.Params))
+func Int64(ctx mctx.Context, name string, defaultVal int64, usage string) *int64 {
-	for _, p := range c.Params {
-		params = append(params, p)
-	}
-
-	for _, child := range c.Children {
-		params = append(params, child.allParams()...)
-	}
-	return params
-}
-
-// ParamInt64 returns an *int64 which will be populated once the Cfg is run
-func (c *Cfg) ParamInt64(name string, defaultVal int64, usage string) *int64 {
 	i := defaultVal
-	c.ParamAdd(Param{Name: name, Usage: usage, Into: &i})
+	MustAdd(ctx, Param{Name: name, Usage: usage, Into: &i})
 	return &i
 }
 
-// ParamRequiredInt64 returns an *int64 which will be populated once the Cfg is
+// RequiredInt64 returns an *int64 which will be populated once Populate is run,
-// run, and which must be supplied by a configuration Source
+// and which must be supplied by a configuration Source.
-func (c *Cfg) ParamRequiredInt64(name string, usage string) *int64 {
+func RequiredInt64(ctx mctx.Context, name string, usage string) *int64 {
 	var i int64
-	c.ParamAdd(Param{Name: name, Required: true, Usage: usage, Into: &i})
+	MustAdd(ctx, Param{Name: name, Required: true, Usage: usage, Into: &i})
 	return &i
 }
 
-// ParamInt returns an *int which will be populated once the Cfg is run
+// Int returns an *int which will be populated once Populate is run.
-func (c *Cfg) ParamInt(name string, defaultVal int, usage string) *int {
+func Int(ctx mctx.Context, name string, defaultVal int, usage string) *int {
 	i := defaultVal
-	c.ParamAdd(Param{Name: name, Usage: usage, Into: &i})
+	MustAdd(ctx, Param{Name: name, Usage: usage, Into: &i})
 	return &i
 }
 
-// ParamRequiredInt returns an *int which will be populated once the Cfg is run,
+// RequiredInt returns an *int which will be populated once Populate is run, and
-// and which must be supplied by a configuration Source
+// which must be supplied by a configuration Source.
-func (c *Cfg) ParamRequiredInt(name string, usage string) *int {
+func RequiredInt(ctx mctx.Context, name string, usage string) *int {
 	var i int
-	c.ParamAdd(Param{Name: name, Required: true, Usage: usage, Into: &i})
+	MustAdd(ctx, Param{Name: name, Required: true, Usage: usage, Into: &i})
 	return &i
 }
 
-// ParamString returns a *string which will be populated once the Cfg is run
+// String returns a *string which will be populated once Populate is run.
-func (c *Cfg) ParamString(name, defaultVal, usage string) *string {
+func String(ctx mctx.Context, name, defaultVal, usage string) *string {
 	s := defaultVal
-	c.ParamAdd(Param{Name: name, Usage: usage, IsString: true, Into: &s})
+	MustAdd(ctx, Param{Name: name, Usage: usage, IsString: true, Into: &s})
 	return &s
 }
 
-// ParamRequiredString returns a *string which will be populated once the Cfg is
+// RequiredString returns a *string which will be populated once Populate is
-// run, and which must be supplied by a configuration Source
+// run, and which must be supplied by a configuration Source.
-func (c *Cfg) ParamRequiredString(name, usage string) *string {
+func RequiredString(ctx mctx.Context, name, usage string) *string {
 	var s string
-	c.ParamAdd(Param{Name: name, Required: true, Usage: usage, IsString: true, Into: &s})
+	MustAdd(ctx, Param{Name: name, Required: true, Usage: usage, IsString: true, Into: &s})
 	return &s
 }
 
-// ParamBool returns a *bool which will be populated once the Cfg is run, and
+// Bool returns a *bool which will be populated once Populate is run, and which
-// which defaults to false if unconfigured
+// 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 (c *Cfg) ParamBool(name, usage string) *bool {
+func Bool(ctx mctx.Context, name, usage string) *bool {
 	var b bool
-	c.ParamAdd(Param{Name: name, Usage: usage, IsBool: true, Into: &b})
+	MustAdd(ctx, Param{Name: name, Usage: usage, IsBool: true, Into: &b})
 	return &b
 }
 
-// ParamTS returns an *mtime.TS which will be populated once the Cfg is run
+// TS returns an *mtime.TS which will be populated once Populate is run.
-func (c *Cfg) ParamTS(name string, defaultVal mtime.TS, usage string) *mtime.TS {
+func TS(ctx mctx.Context, name string, defaultVal mtime.TS, usage string) *mtime.TS {
 	t := defaultVal
-	c.ParamAdd(Param{Name: name, Usage: usage, Into: &t})
+	MustAdd(ctx, Param{Name: name, Usage: usage, Into: &t})
 	return &t
 }
 
-// ParamDuration returns an *mtime.Duration which will be populated once the Cfg
+// RequiredTS returns an *mtime.TS which will be populated once Populate is run,
-// is run
+// and which must be supplied by a configuration Source.
-func (c *Cfg) ParamDuration(name string, defaultVal mtime.Duration, usage string) *mtime.Duration {
+func RequiredTS(ctx mctx.Context, name, usage string) *mtime.TS {
+	var t mtime.TS
+	MustAdd(ctx, Param{Name: name, Required: true, Usage: usage, Into: &t})
+	return &t
+}
+
+// Duration returns an *mtime.Duration which will be populated once
+// Populate is run.
+func Duration(ctx mctx.Context, name string, defaultVal mtime.Duration, usage string) *mtime.Duration {
 	d := defaultVal
-	c.ParamAdd(Param{Name: name, Usage: usage, IsString: true, Into: &d})
+	MustAdd(ctx, Param{Name: name, Usage: usage, IsString: true, Into: &d})
 	return &d
 }
 
-// ParamJSON reads the parameter value as a JSON value and unmarshals it into
+// RequiredDuration returns an *mtime.Duration which will be populated once
-// the given interface{} (which should be a pointer). The receiver (into) is
+// Populate is run, and which must be supplied by a configuration Source.
-// also used to determine the default value.
+func RequiredDuration(ctx mctx.Context, name string, defaultVal mtime.Duration, usage string) *mtime.Duration {
-func (c *Cfg) ParamJSON(name string, into interface{}, usage string) {
+	var d mtime.Duration
-	c.ParamAdd(Param{Name: name, Usage: usage, Into: into})
+	MustAdd(ctx, Param{Name: name, Required: true, Usage: usage, IsString: true, Into: &d})
+	return &d
 }
 
-// ParamRequiredJSON reads the parameter value as a JSON value and unmarshals it
+// JSON reads the parameter value as a JSON value and unmarshals it into the
-// into the given interface{} (which should be a pointer).
+// given interface{} (which should be a pointer). The receiver (into) is also
-func (c *Cfg) ParamRequiredJSON(name string, into interface{}, usage string) {
+// used to determine the default value.
-	c.ParamAdd(Param{Name: name, Required: true, Usage: usage, Into: into})
+func JSON(ctx mctx.Context, name string, into interface{}, usage string) {
+	MustAdd(ctx, Param{Name: name, Usage: usage, Into: into})
+}
+
+// RequiredJSON 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 RequiredJSON(ctx mctx.Context, name string, into interface{}, usage string) {
+	MustAdd(ctx, Param{Name: name, Required: true, Usage: usage, Into: into})
 }

mcfg/source.go

@@ -5,28 +5,30 @@ import (
 )
 
 // ParamValue describes a value for a parameter which has been parsed by a
-// Source
+// Source.
 type ParamValue struct {
 	Param
 	Value json.RawMessage
 }
 
-// Source parses ParamValues out of a particular configuration source. The
+// Source parses ParamValues out of a particular configuration source, given a
-// returned []ParamValue may contain duplicates of the same Param's value.
+// sorted set of possible Params to parse. The returned []ParamValue may contain
+// duplicates of the same Param's value. in which case the later value takes
+// precedence.
 type Source interface {
-	Parse(*Cfg) ([]ParamValue, error)
+	Parse([]Param) ([]ParamValue, error)
 }
 
 // Sources combines together multiple Source instances into one. It will call
-// Parse on each element individually. Later Sources take precedence over
+// Parse on each element individually. Values from later Sources take precedence
-// previous ones in the slice.
+// over previous ones.
 type Sources []Source
 
 // Parse implements the method for the Source interface.
-func (ss Sources) Parse(c *Cfg) ([]ParamValue, error) {
+func (ss Sources) Parse(params []Param) ([]ParamValue, error) {
 	var pvs []ParamValue
 	for _, s := range ss {
-		innerPVs, err := s.Parse(c)
+		innerPVs, err := s.Parse(params)
 		if err != nil {
 			return nil, err
 		}
@@ -37,13 +39,14 @@ func (ss Sources) Parse(c *Cfg) ([]ParamValue, error) {
 
 // SourceMap implements the Source interface by mapping parameter names to
 // values for them. The names are comprised of the path and name of a Param
-// joined by "-" characters, i.e. `strings.Join(append(p.Path, p.Name), "-")`.
+// joined by "-" characters, i.e. `strings.Join(append(param.Path, param.Name),
-// Values will be parsed in the same way that SourceEnv parses its variables.
+// "-")`.  Values will be parsed in the same way that SourceEnv parses its
+// variables.
 type SourceMap map[string]string
 
-func (m SourceMap) Parse(c *Cfg) ([]ParamValue, error) {
+func (m SourceMap) Parse(params []Param) ([]ParamValue, error) {
 	pvs := make([]ParamValue, 0, len(m))
-	for _, p := range c.allParams() {
+	for _, p := range params {
 		if v, ok := m[p.fullName()]; ok {
 			pvs = append(pvs, ParamValue{
 				Param: p,

mcfg/source_test.go

@@ -6,6 +6,7 @@ import (
 	. "testing"
 	"time"
 
+	"github.com/mediocregopher/mediocre-go-lib/mctx"
 	"github.com/mediocregopher/mediocre-go-lib/mrand"
 	"github.com/mediocregopher/mediocre-go-lib/mtest/massert"
 )
@@ -15,8 +16,8 @@ import (
 // all the code they share
 
 type srcCommonState struct {
-	cfg       *Cfg
+	ctx       mctx.Context
-	availCfgs []*Cfg
+	availCtxs []mctx.Context
 	expPVs    []ParamValue
 
 	// each specific test should wrap this to add the Source itself
@@ -24,22 +25,22 @@ type srcCommonState struct {
 
 func newSrcCommonState() srcCommonState {
 	var scs srcCommonState
-	scs.cfg = New()
+	scs.ctx = mctx.New()
 	{
-		a := scs.cfg.Child("a")
+		a := mctx.ChildOf(scs.ctx, "a")
-		b := scs.cfg.Child("b")
+		b := mctx.ChildOf(scs.ctx, "b")
-		c := scs.cfg.Child("c")
+		c := mctx.ChildOf(scs.ctx, "c")
-		ab := a.Child("b")
+		ab := mctx.ChildOf(a, "b")
-		bc := b.Child("c")
+		bc := mctx.ChildOf(b, "c")
-		abc := ab.Child("c")
+		abc := mctx.ChildOf(ab, "c")
-		scs.availCfgs = []*Cfg{scs.cfg, a, b, c, ab, bc, abc}
+		scs.availCtxs = []mctx.Context{scs.ctx, a, b, c, ab, bc, abc}
 	}
 	return scs
 }
 
 type srcCommonParams struct {
 	name        string
-	availCfgI   int // not technically needed, but finding the cfg easier
+	availCtxI   int // not technically needed, but makes finding the ctx easier
 	path        []string
 	isBool      bool
 	nonBoolType string // "int", "str", "duration", "json"
@@ -55,9 +56,9 @@ func (scs srcCommonState) next() srcCommonParams {
 		p.name = mrand.Hex(8)
 	}
 
-	p.availCfgI = mrand.Intn(len(scs.availCfgs))
+	p.availCtxI = mrand.Intn(len(scs.availCtxs))
-	thisCfg := scs.availCfgs[p.availCfgI]
+	thisCtx := scs.availCtxs[p.availCtxI]
-	p.path = thisCfg.Path
+	p.path = mctx.Path(thisCtx)
 
 	p.isBool = mrand.Intn(2) == 0
 	if !p.isBool {
@@ -93,22 +94,22 @@ func (scs srcCommonState) next() srcCommonParams {
 	return p
 }
 
-// adds the new cfg param to the cfg, and if the param is expected to be set in
+// adds the new param to the ctx, and if the param is expected to be set in
 // the Source adds it to the expected ParamValues as well
-func (scs srcCommonState) applyCfgAndPV(p srcCommonParams) srcCommonState {
+func (scs srcCommonState) applyCtxAndPV(p srcCommonParams) srcCommonState {
-	thisCfg := scs.availCfgs[p.availCfgI]
+	thisCtx := scs.availCtxs[p.availCtxI]
-	cfgP := Param{
+	ctxP := 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 Cfg once it has all ParamValues together
+		// those are only used by Populate once it has all ParamValues together
 	}
-	thisCfg.ParamAdd(cfgP)
+	MustAdd(thisCtx, ctxP)
-	cfgP = thisCfg.Params[p.name] // get it back out to get any added fields
+	ctxP = get(thisCtx).params[p.name] // get it back out to get any added fields
 
 	if !p.unset {
-		pv := ParamValue{Param: cfgP}
+		pv := ParamValue{Param: ctxP}
 		if p.isBool {
 			pv.Value = json.RawMessage("true")
 		} else {
@@ -130,7 +131,7 @@ func (scs srcCommonState) applyCfgAndPV(p srcCommonParams) srcCommonState {
 // given a Source asserts that it's Parse method returns the expected
 // ParamValues
 func (scs srcCommonState) assert(s Source) error {
-	gotPVs, err := s.Parse(scs.cfg)
+	gotPVs, err := s.Parse(collectParams(scs.ctx))
 	if err != nil {
 		return err
 	}
@@ -141,12 +142,12 @@ func (scs srcCommonState) assert(s Source) error {
 }
 
 func TestSources(t *T) {
-	cfg := New()
+	ctx := mctx.New()
-	a := cfg.ParamRequiredInt("a", "")
+	a := RequiredInt(ctx, "a", "")
-	b := cfg.ParamRequiredInt("b", "")
+	b := RequiredInt(ctx, "b", "")
-	c := cfg.ParamRequiredInt("c", "")
+	c := RequiredInt(ctx, "c", "")
 
-	err := cfg.populateParams(Sources{
+	err := Populate(ctx, Sources{
 		SourceCLI{Args: []string{"--a=1", "--b=666"}},
 		SourceEnv{Env: []string{"B=2", "C=3"}},
 	})
@@ -159,13 +160,13 @@ func TestSources(t *T) {
 }
 
 func TestSourceMap(t *T) {
-	cfg := New()
+	ctx := mctx.New()
-	a := cfg.ParamRequiredInt("a", "")
+	a := RequiredInt(ctx, "a", "")
-	foo := cfg.Child("foo")
+	foo := mctx.ChildOf(ctx, "foo")
-	b := foo.ParamRequiredString("b", "")
+	b := RequiredString(foo, "b", "")
-	c := foo.ParamBool("c", "")
+	c := Bool(foo, "c", "")
 
-	err := cfg.populateParams(SourceMap{
+	err := Populate(ctx, SourceMap{
 		"a":     "4",
 		"foo-b": "bbb",
 		"foo-c": "1",