Golang : does not implement flag.Value (missing Set method)
Keep getting this error message : does not implement flag.Value (missing Set method) while trying to write example for flag.Var() function today. Apparently, to assign value with flag.Var() function to a variable in a struct. You need to implement Set() and Get() method. It is helpful to have String() method as well.
To fix this error, all you need to do is the add the Set method.
For example :
package main
import (
"flag"
"fmt"
)
type flagStr struct {
value *string
}
// compiler will throw out missing Set method
// if this method below is ... well.. missing
func (f *flagStr) Set(value string) error {
f.value = &value
return nil
}
func (f *flagStr) Get() *string {
return f.value
}
func (f *flagStr) String() string {
if f.value != nil {
return *f.value
}
return ""
}
var (
appFlags struct {
appID flagStr
appSecret flagStr
}
)
func main() {
flag.Var(&appFlags.appID, "FBAppID", "Facebook Application ID")
appFlags.appID.Set("1234567890")
flag.Var(&appFlags.appSecret, "FBAppSecret", "Facebook Application Secret")
flag.Parse()
fmt.Println(flag.Lookup("FBAppID")) // print the Flag struct
fmt.Println(&appFlags.appID)
}
By Adam Ng
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