How to pass a struct's method as a parameter into another function using golang

Question

Sorry, I post my question again.

I have been read the solution before I ask my question. I think it can not help me because my question is how to pass a function as a parameter? I don't want to call it.

I just want to pass it to another function that I can't edit (or I don't want to edit), and I want to use a string variable to point the function

funcName := "Go"
 m.set(t.funcName)

I think this is different from this question Call a Struct and its Method by name in Go?

for example

I have a function like:

type Context struct{}
type myclass struct{}
type Handler func (c *Context)

func (r *myclass) set(ch Handler)  {

}

I can use this way:

type testclass struct {}
func (t *testclass) Go(c *Context){
    println("Hello");
}

t := &testclass{}
m := &myclass{}
m.set(t.Go)

and my question is

type testclass struct{}
func (t *testclass) Go(c *Context){
    println("Hello");
}

t := &testclass{}
m := &myclass{}

funcName := "Go"
m.set(t.funcName)

any way can do this?

reflect?or what?

if it is impossible, there are other ways to do this?

thanks

What are you trying to do? Why do you want to do this? – peterSO Mar 07 '16 at 06:19 — peterSO, Mar 07 '16 at 06:19

Charlie Tumahai · Answer 1 · 2016-03-07T15:02:46.377

0

You can get the method by name using the reflect package. Here's a function to get a Handler given the name:

func handlerByName(v interface{}, name string) (Handler, error) {
  m := reflect.ValueOf(v).MethodByName(name)
  if !m.IsValid() {
    return nil, errors.New("method not found")
  }
  h, ok := m.Interface().(func(*Context))
  if !ok {
    return nil, errors.New("method is not a handler")
  }
  return h, nil
}

Here's how to use the function:

h, err := handlerByName(t, "Go")
if err != nil {
   // handle error
}
m.set(h)

playground example

Note that the function returned by handlerByName is a reflection wrapper around the original function (thanks @OneOfOne for pointing this out). Calling the wrapper is slow compared to calling the function directly.

edited Mar 07 '16 at 15:02

answered Mar 07 '16 at 06:20

Charlie Tumahai

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You should add that this isn't very idiomatic (or safe) code. The OP's code could probably avoid this if we had more context around the "why". – elithrar Mar 07 '16 at 08:15
The OP presumably is not an advanced Go user. Why do you recommend using reflection? – Volker Mar 07 '16 at 09:37
@Volker The suitability of reflection for a given task is independent of the person asking. – Charlie Tumahai Mar 07 '16 at 13:51
@elithrar I updated the code to make it safe. Thanks for the feedback. – Charlie Tumahai Mar 07 '16 at 13:53
Also note that using reflection to call methods/funcs is extremely slow because of the added wrappers. – OneOfOne Mar 07 '16 at 14:14
@OneOfOne Reflection does not add any wrappers around the function returned from `handlerByName`. There is a cost to finding the function using reflection, but that cost is not extreme compared to other possible ways to find a function given a string. – Charlie Tumahai Mar 07 '16 at 14:34
@OneOfOne Thank you for that. Do you know where in the reflect code the wrapper is added? – Charlie Tumahai Mar 07 '16 at 14:50
@Volker yes, I just study golang about few days, you may think Im not qualified enough but I just want to write a web framework for myself, I know this is not a easy work but I will try my best – herb Mar 08 '16 at 02:15

How to pass a struct's method as a parameter into another function using golang

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