docker-machine/vendor/github.com/mitchellh/mapstructure/decode_hooks.go

package mapstructure

import (
	"reflect"
	"strconv"
	"strings"
)

// ComposeDecodeHookFunc creates a single DecodeHookFunc that
// automatically composes multiple DecodeHookFuncs.
//
// The composed funcs are called in order, with the result of the
// previous transformation.
func ComposeDecodeHookFunc(fs ...DecodeHookFunc) DecodeHookFunc {
	return func(
		f reflect.Kind,
		t reflect.Kind,
		data interface{}) (interface{}, error) {
		var err error
		for _, f1 := range fs {
			data, err = f1(f, t, data)
			if err != nil {
				return nil, err
			}

			// Modify the from kind to be correct with the new data
			f = getKind(reflect.ValueOf(data))
		}

		return data, nil
	}
}

// StringToSliceHookFunc returns a DecodeHookFunc that converts
// string to []string by splitting on the given sep.
func StringToSliceHookFunc(sep string) DecodeHookFunc {
	return func(
		f reflect.Kind,
		t reflect.Kind,
		data interface{}) (interface{}, error) {
		if f != reflect.String || t != reflect.Slice {
			return data, nil
		}

		raw := data.(string)
		if raw == "" {
			return []string{}, nil
		}

		return strings.Split(raw, sep), nil
	}
}

func WeaklyTypedHook(
	f reflect.Kind,
	t reflect.Kind,
	data interface{}) (interface{}, error) {
	dataVal := reflect.ValueOf(data)
	switch t {
	case reflect.String:
		switch f {
		case reflect.Bool:
			if dataVal.Bool() {
				return "1", nil
			} else {
				return "0", nil
			}
		case reflect.Float32:
			return strconv.FormatFloat(dataVal.Float(), 'f', -1, 64), nil
		case reflect.Int:
			return strconv.FormatInt(dataVal.Int(), 10), nil
		case reflect.Slice:
			dataType := dataVal.Type()
			elemKind := dataType.Elem().Kind()
			if elemKind == reflect.Uint8 {
				return string(dataVal.Interface().([]uint8)), nil
			}
		case reflect.Uint:
			return strconv.FormatUint(dataVal.Uint(), 10), nil
		}
	}

	return data, nil
}