Go Flag Usage Description Contains the Word value-CodePudding

I've defined a custom flag for accepting a slice of strings as such:

type strSliceFlag []string

func (i *strSliceFlag) String() string {
    return fmt.Sprint(*i)
}

func (i *strSliceFlag) Set(value string) error {
    *i = append(*i, value)
    return nil
}

I then parse it with

    ...
    var tags strSliceFlag
    flag.Var(&tags, "t", tFlagExpl)
    flag.Parse()
    ...

When I build this program, and run it with the help flag: main -h, it prints out:

Usage of main:
  -t value
        Test explanation

My question is, where is the word value coming from? I can't find out how to remove it. I think it maybe has something to do with the default value for the flag.

CodePudding user response：

value is the default argument name chosen by flag.UnquoteUsage for custom types (rendered via flag.(*FlagSet).PrintDefaults).

You can override the default with backquotes in your usage text. The backquotes are stripped from usage text. Eg:

package main

import (
    "flag"
    "fmt"
)

type stringSlice []string

func (s *stringSlice) String() string {
    return fmt.Sprint(*s)
}

func (s *stringSlice) Set(v string) error {
    *s = append(*s, v)
    return nil
}

func main() {
    var s stringSlice
    flag.Var(&s, "foo", "append a foo to the list")
    flag.Var(&s, "foo2", "append a `foo` to the list")
    flag.Parse()
}

Running with -h shows how the argument name changes:

Usage of ./flagusage:
  -foo value
        append a foo to the list
  -foo2 foo
        append a foo to the list