Clean up decoders a bit.

build.go

@@ -37,7 +37,10 @@ func buildNode(v reflect.Value) *Node {
 			name = strings.ToLower(strings.Join(camelCase(ft.Name), "-"))
 		}
 		help := ft.Tag.Get("help")
-		decoder := DecoderForField(ft)
+		decoder, err := DecoderForField(ft)
+		if err != nil && ft.Type.Kind() != reflect.Struct {
+			panic(err)
+		}
 		dflt := ft.Tag.Get("default")
 		placeholder := ft.Tag.Get("placeholder")
 		if placeholder == "" {

decoders.go

@@ -85,26 +85,25 @@ var (
 )
 
 // DecoderForField finds a decoder for a struct field.
-//
-func DecoderForField(field reflect.StructField) Decoder {
+func DecoderForField(field reflect.StructField) (Decoder, error) {
 	name, ok := field.Tag.Lookup("type")
 	if ok {
 		if decoder, ok := namedDecoders[name]; ok {
-			return decoder
+			return decoder, nil
 		}
 	}
 	return DecoderForType(field.Type)
 }
 
-func DecoderForType(typ reflect.Type) Decoder {
+func DecoderForType(typ reflect.Type) (Decoder, error) {
 	var decoder Decoder
 	var ok bool
 	if decoder, ok = typeDecoders[typ]; ok {
-		return decoder
+		return decoder, nil
 	} else if decoder, ok = kindDecoders[typ.Kind()]; ok {
-		return decoder
+		return decoder, nil
 	}
-	return missingDecoder
+	return nil, fmt.Errorf("no decoder for type %s", typ)
 }
 
 // RegisterDecoder registers decoders.
@@ -126,49 +125,19 @@ func RegisterDecoder(decoders ...Decoder) {
 }
 
 func init() {
-	intDecoder := NewKindDecoder(reflect.Int, func(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
-		n, err := strconv.ParseInt(scan.PopValue("int"), 10, 64)
-		if err != nil {
-			return err
-		}
-		target.SetInt(n)
-		return nil
-	})
-	uintDecoder := NewKindDecoder(reflect.Uint, func(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
-		n, err := strconv.ParseUint(scan.PopValue("uint"), 10, 64)
-		if err != nil {
-			return err
-		}
-		target.SetUint(n)
-		return nil
-	})
 	kindDecoders = map[reflect.Kind]KindDecoder{
-		reflect.Int:    intDecoder,
-		reflect.Int8:   intDecoder,
-		reflect.Int16:  intDecoder,
-		reflect.Int32:  intDecoder,
-		reflect.Int64:  intDecoder,
-		reflect.Uint:   uintDecoder,
-		reflect.Uint8:  uintDecoder,
-		reflect.Uint16: uintDecoder,
-		reflect.Uint32: uintDecoder,
-		reflect.Uint64: uintDecoder,
-		reflect.Float32: NewKindDecoder(reflect.Float32, func(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
-			n, err := strconv.ParseFloat(scan.PopValue("float"), 32)
-			if err != nil {
-				return err
-			}
-			target.SetFloat(n)
-			return nil
-		}),
-		reflect.Float64: NewKindDecoder(reflect.Float64, func(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
-			n, err := strconv.ParseFloat(scan.PopValue("float"), 64)
-			if err != nil {
-				return err
-			}
-			target.SetFloat(n)
-			return nil
-		}),
+		reflect.Int:     NewKindDecoder(reflect.Int, intDecoder),
+		reflect.Int8:    NewKindDecoder(reflect.Int8, intDecoder),
+		reflect.Int16:   NewKindDecoder(reflect.Int16, intDecoder),
+		reflect.Int32:   NewKindDecoder(reflect.Int32, intDecoder),
+		reflect.Int64:   NewKindDecoder(reflect.Int64, intDecoder),
+		reflect.Uint:    NewKindDecoder(reflect.Uint, uintDecoder),
+		reflect.Uint8:   NewKindDecoder(reflect.Uint8, uintDecoder),
+		reflect.Uint16:  NewKindDecoder(reflect.Uint16, uintDecoder),
+		reflect.Uint32:  NewKindDecoder(reflect.Uint32, uintDecoder),
+		reflect.Uint64:  NewKindDecoder(reflect.Uint64, uintDecoder),
+		reflect.Float32: NewKindDecoder(reflect.Float32, floatDecoder(32)),
+		reflect.Float64: NewKindDecoder(reflect.Float64, floatDecoder(64)),
 		reflect.String: NewKindDecoder(reflect.String, func(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
 			target.SetString(scan.PopValue("string"))
 			return nil
@@ -177,27 +146,57 @@ func init() {
 			target.SetBool(true)
 			return nil
 		}),
-		reflect.Slice: NewKindDecoder(reflect.Slice, func(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
-			el := target.Type().Elem()
-			sep, ok := ctx.Value.Field.Tag.Lookup("sep")
-			if !ok {
-				sep = ","
-			}
-			childScanner := Scan(strings.Split(scan.PopValue("slice"), sep)...)
-			childDecoder := DecoderForType(el)
-			for childScanner.Peek().Type != EOLToken {
-				childValue := reflect.New(el).Elem()
-				err := childDecoder.Decode(ctx, childScanner, childValue)
-				if err != nil {
-					return err
-				}
-				target.Set(reflect.Append(target, childValue))
-			}
-			return nil
-		}),
+		reflect.Slice: NewKindDecoder(reflect.Slice, sliceDecoder),
 	}
 }
 
-var missingDecoder DecoderFunc = func(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
-	return fmt.Errorf("no decoder for %q (of type %T) for field %q", target.String(), target.Type(), ctx.Value.Field.Name)
+func intDecoder(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
+	n, err := strconv.ParseInt(scan.PopValue("int"), 10, 64)
+	if err != nil {
+		return err
+	}
+	target.SetInt(n)
+	return nil
+}
+
+func uintDecoder(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
+	n, err := strconv.ParseUint(scan.PopValue("uint"), 10, 64)
+	if err != nil {
+		return err
+	}
+	target.SetUint(n)
+	return nil
+}
+
+func floatDecoder(bits int) DecoderFunc {
+	return func(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
+		n, err := strconv.ParseFloat(scan.PopValue("float"), bits)
+		if err != nil {
+			return err
+		}
+		target.SetFloat(n)
+		return nil
+	}
+}
+
+func sliceDecoder(ctx *DecoderContext, scan *Scanner, target reflect.Value) error {
+	el := target.Type().Elem()
+	sep, ok := ctx.Value.Field.Tag.Lookup("sep")
+	if !ok {
+		sep = ","
+	}
+	childScanner := Scan(strings.Split(scan.PopValue("list"), sep)...)
+	childDecoder, err := DecoderForType(el)
+	if err != nil {
+		return err
+	}
+	for childScanner.Peek().Type != EOLToken {
+		childValue := reflect.New(el).Elem()
+		err := childDecoder.Decode(ctx, childScanner, childValue)
+		if err != nil {
+			return err
+		}
+		target.Set(reflect.Append(target, childValue))
+	}
+	return nil
 }