Function call by name in Golang

The golang’s function is a code block like C’s, but it can also be assigned to a variable as its other types.

If you are not familiar with the function, Codewalk: First-Class Functions in Go should be a good starting point for you. Already known it? Let’s go on.

First of all, look at this PHP codes:

function foobar() {
    echo "Hello Golang\n";
$funcs = array(
    "foobar" => "foobar",
    "hello"  => "foobar",

It will print:

mikespook@mikespook-laptop:~/Desktop$ php foobar.php 
Hello Golang
Hello Golang

It is very useful for calling a function with name matching.

So, is it possible to call a function by its name in Golang?
As a static, compiled programming language, the answer is No … and YES!

You can not do this in Golang:

func foobar() {
    // bla...bla...bla...
funcname := "foobar"

You can do:

func foobar() {
    // bla...bla...bla...
funcs := map[string]func() {"foobar":foobar}

But here’s a limitation that the map only work with the prototype “func()”, no input parameters and return arguments.
If you want to call some functions have different function’s prototypes, the interface{} should be used.

Yep! interface{}, like the void pointer in C. Remember that? No? Never mind! Read this: The Go Programming Language Specification:Interface types.

Then we could add functions with different prototypes into one map:

func foo() {
    // bla...bla...bla...
func bar(a, b, c int) {
    // bla...bla...bla...
funcs := map[string]interface{}{"foo":foo, "bar":bar}

How to call a function in the map? like this?


NO! It does not work! You can not call a function stored in a empty interface variable directly.

Reflection comes to us! It is a package called “reflect” in Golang. Do you know reflection already?
If not, just read this: Laws of reflection.

func Call(m map[string]interface{}, name string, params ... interface{}) (result []reflect.Value, err error) {
    f = reflect.ValueOf(m[name])
    if len(params) != f.Type().NumIn() {
        err = errors.New("The number of params is not adapted.")
    in := make([]reflect.Value, len(params))
    for k, param := range params {
        in[k] = reflect.ValueOf(param)
    result = f.Call(in)
Call(funcs, "foo")
Call(funcs, "bar", 1, 2, 3)

Reflecting the function variable, use reflect.Call to call it and pass parameters into it at the same time.
Nothing could be hard to understand.

I’ve done a package for this functional:

Hope this helps. Have a good time, gophers!

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  1. 所有涉及到go的函数均应该为func关键字而非function:比如:
    function foo() {
    // bla…bla…bla…
    function bar(a, b, c int) {
    // bla…bla…bla…

  2. How about:

    package mypackage

    func foo (s string, i int) (bool, error) {
    return false, nil

    func bar (opts []string) (int, error) {
    return 456, nil

    var Foo func(string, int) (bool, error)
    var Bar func([]string) (int, error)

    func init() {
    Foo = foo
    Bar = bar

    func main() {
    b, err := Foo(“abc”, 345)
    i, err := Bar([]string{“abc”, “edf”})

    You could use this for exporting private functions only for testing f.i..


  3. Possible func variable value default?

    func foo (s string = “test”, i int = 1) (bool, error)

    How to do? its not work

  4. There is no default variable value for functions in Golang. If you want to do so, the `reflect` package may be the only choice for you. You can write a warp function which detects if the params are zero value, and then set a default value.

  5. Good article. I’m getting this error in your last example:
    cannot use funcs (type map[string]func()) as type map[string]interface {} in argument to Call

    // Invoke – firstResult, err := invoke(AnyStructInterface, MethodName, Params…)
    func Invoke(any interface{}, name string, args …interface{}) (reflect.Value, error) {
    method := reflect.ValueOf(any).MethodByName(name)
    methodType := method.Type()
    numIn := methodType.NumIn()
    if numIn > len(args) {
    return reflect.ValueOf(nil), fmt.Errorf(“Method %s must have minimum %d params. Have %d”, name, numIn, len(args))
    if numIn != len(args) && !methodType.IsVariadic(){
    return reflect.ValueOf(nil), fmt.Errorf(“Method %s must have %d params. Have %d”, name, numIn, len(args))
    in := make([]reflect.Value, len(args))
    for i := 0; i = numIn-1 {
    inType = methodType.In(numIn – 1).Elem()
    } else {
    inType = methodType.In(i)
    argValue := reflect.ValueOf(args[i])
    argType := argValue.Type()
    if argType.ConvertibleTo(inType) {
    in[i] = argValue.Convert(inType)
    } else {
    return reflect.ValueOf(nil), fmt.Errorf(“Method %s. Param[%d] must be %s. Have %s”, name, i, inType, argType)
    return method.Call(in)[0], nil

  7. Thanks! This is the way to call methods of a struct by name.
    However, it won’t work with normal functions.
    BTW, the last return statement `method.Call(in)[0]`, the element length should be checked if equals 0 or not.

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