mcfg: add some helper methods to Cfg related to its Path

mcfg/cli.go

@@ -124,7 +124,7 @@ func (cli SourceCLI) cliParamVals(cfg *Cfg) (map[string]ParamValue, error) {
 	m := map[string]ParamValue{}
 	for _, param := range cfg.Params {
 		key := cliKeyPrefix
-		if len(cfg.Path) > 0 {
+		if !cfg.IsRoot() {
 			key += strings.Join(cfg.Path, cliKeyJoin) + cliKeyJoin
 		}
 		key += param.Name

mcfg/mcfg.go

@@ -6,6 +6,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"strings"
 )
 
 // TODO Sources:
@@ -120,6 +121,27 @@ func New() *Cfg {
 	}
 }
 
+// IsRoot returns true if this is the root instance of a Cfg (i.e. the one
+// returned by New)
+func (c *Cfg) IsRoot() bool {
+	return len(c.Path) == 0
+}
+
+// Name returns the name given to this instance when it was created via Child.
+// if this instance was created via New (i.e. it is the root instance) then
+// 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 {
 	// we allow for nil Source here for tests
 	// TODO make Source stub type which tests could use here instead

mcfg/mcfg_test.go

@@ -120,3 +120,25 @@ 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())
+}