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
IF you gain some knowledge or the information here solved your programming problem. Please consider donating to the less fortunate or some charities that you like. Apart from donation, planting trees, volunteering or reducing your carbon footprint will be great too.
Advertisement
Tutorials
+4.3k PageSpeed : Clear or flush cache on web server
+3.3k Unix/Linux : How to pipe/save output of a command to file?
+3k Python : Find out the variable type and determine the type with simple test
+23.2k Golang : Smarter Error Handling with strings.Contains()
+9.3k Golang : Get month name from date example
+17k Golang : Set or Add HTTP Request Headers
+10.3k Golang : Convert spaces to tabs and back to spaces example
+16.6k Golang : Execute shell command
+9.7k Golang : Convert IPv4 address to packed 32-bit binary format
+3.9k Fix yum-complete-transaction error
+9.1k Golang : Convert a rune to unicode style string \u
+6.3k Golang : Sort lines of text example