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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package pflag
import (
goflag "flag"
// flagValueWrapper implements pflag.Value around a flag.Value. The main
// difference here is the addition of the Type method that returns a string
// name of the type. As this is generally unknown, we approximate that with
// reflection.
type flagValueWrapper struct {
inner goflag.Value
flagType string
// We are just copying the boolFlag interface out of goflag as that is what
// they use to decide if a flag should get "true" when no arg is given.
type goBoolFlag interface {
IsBoolFlag() bool
func wrapFlagValue(v goflag.Value) Value {
// If the flag.Value happens to also be a pflag.Value, just use it directly.
if pv, ok := v.(Value); ok {
return pv
pv := &flagValueWrapper{
inner: v,
t := reflect.TypeOf(v)
if t.Kind() == reflect.Interface || t.Kind() == reflect.Ptr {
t = t.Elem()
pv.flagType = strings.TrimSuffix(t.Name(), "Value")
return pv
func (v *flagValueWrapper) String() string {
return v.inner.String()
func (v *flagValueWrapper) Set(s string) error {
return v.inner.Set(s)
func (v *flagValueWrapper) Type() string {
return v.flagType
// PFlagFromGoFlag will return a *pflag.Flag given a *flag.Flag
// If the *flag.Flag.Name was a single character (ex: `v`) it will be accessiblei
// with both `-v` and `--v` in flags. If the golang flag was more than a single
// character (ex: `verbose`) it will only be accessible via `--verbose`
func PFlagFromGoFlag(goflag *goflag.Flag) *Flag {
// Remember the default value as a string; it won't change.
flag := &Flag{
Name: goflag.Name,
Usage: goflag.Usage,
Value: wrapFlagValue(goflag.Value),
// Looks like golang flags don't set DefValue correctly :-(
//DefValue: goflag.DefValue,
DefValue: goflag.Value.String(),
// Ex: if the golang flag was -v, allow both -v and --v to work
if len(flag.Name) == 1 {
flag.Shorthand = flag.Name
if fv, ok := goflag.Value.(goBoolFlag); ok && fv.IsBoolFlag() {
flag.NoOptDefVal = "true"
return flag
// AddGoFlag will add the given *flag.Flag to the pflag.FlagSet
func (f *FlagSet) AddGoFlag(goflag *goflag.Flag) {
if f.Lookup(goflag.Name) != nil {
newflag := PFlagFromGoFlag(goflag)
// AddGoFlagSet will add the given *flag.FlagSet to the pflag.FlagSet
func (f *FlagSet) AddGoFlagSet(newSet *goflag.FlagSet) {
if newSet == nil {
newSet.VisitAll(func(goflag *goflag.Flag) {