Add decoders scaffolding.

decoders.go

@@ -0,0 +1,95 @@
+package kong
+
+import "reflect"
+
+type Decoder interface {
+	Decode(input string, target reflect.Value) error
+}
+
+type DecoderFunc func(input string, target reflect.Value) error
+
+func (d DecoderFunc) Decode(input string, target reflect.Value) error { return d(input, target) }
+
+var _ Decoder = DecoderFunc(nil)
+
+type TypeDecoder interface {
+	Type() reflect.Type
+	Decoder
+}
+
+func NewTypeDecoder(typ reflect.Type, decoder DecoderFunc) TypeDecoder {
+	return &typeDecoder{typ, decoder}
+}
+
+type typeDecoder struct {
+	typ reflect.Type
+	DecoderFunc
+}
+
+func (t *typeDecoder) Type() reflect.Type { return t.typ }
+
+var _ TypeDecoder = &typeDecoder{}
+
+type KindDecoder interface {
+	Kind() reflect.Kind
+	Decoder
+}
+
+func NewKindDecoder(kind reflect.Kind, decoder DecoderFunc) KindDecoder {
+	return &kindDecoder{kind, decoder}
+}
+
+type kindDecoder struct {
+	kind reflect.Kind
+	DecoderFunc
+}
+
+func (k *kindDecoder) Kind() reflect.Kind { return k.kind }
+
+var _ KindDecoder = &kindDecoder{}
+
+type NamedDecoder interface {
+	Name() string
+	Decoder
+}
+
+func NewNamedDecoder(name string, decoder DecoderFunc) NamedDecoder {
+	return &namedDecoder{name, decoder}
+}
+
+type namedDecoder struct {
+	name string
+	DecoderFunc
+}
+
+func (n *namedDecoder) Name() string { return n.name }
+
+var _ NamedDecoder = &namedDecoder{}
+
+var (
+	namedDecoders = map[string]NamedDecoder{}
+	typeDecoders  = map[reflect.Type]TypeDecoder{}
+	kindDecoders  = map[reflect.Kind]KindDecoder{}
+)
+
+// RegisterDecoder registers decoders.
+//
+// Decoders must be one of TypeDecoder, KindDecoder or NamedDecoder.
+func RegisterDecoder(decoders ...Decoder) {
+	for _, decoder := range decoders {
+		switch decoder := decoder.(type) {
+		case TypeDecoder:
+			typeDecoders[decoder.Type()] = decoder
+		case KindDecoder:
+			kindDecoders[decoder.Kind()] = decoder
+		case NamedDecoder:
+			namedDecoders[decoder.Name()] = decoder
+		default:
+			panic("unsupported decoder type " + reflect.TypeOf(decoder).String())
+		}
+	}
+}
+
+func init() {
+	RegisterDecoder()
+}

kong.go

@@ -12,15 +12,17 @@ type Kong struct {
 	Terminate func(int)
 }
 
+// New creates a new Kong parser into grammar.
 func New(name, description string, grammar interface{}) (*Kong, error) {
 	if name == "" {
 		name = filepath.Base(os.Args[0])
 	}
+	model := &ApplicationModel{
+		Name:        name,
+		Description: description,
+	}
 	return &Kong{
-		Model: &ApplicationModel{
-			Name:        name,
-			Description: description,
-		},
+		Model:     model,
 		Terminate: os.Exit,
 	}, nil
 }