reflect: add MakeFunc

[bradfitz]

Feature request:

reflect.MakeFunc(Type, func([]Value) []Value)

So one can do:

  var f func(a, b int) string
  embeddedLang.GetFunc("func", &f)
  s := f(1, 2)

[bradfitz]

Comment 1:

with a return value of course:
reflect.MakeFunc(Type, func([]Value) []Value) Value

[robpike]

Comment 2:

This is just some code. I can't see what it's supposed to do. How does it differ from
calling Interface() on a Func Value?
package main
import "fmt"
import "reflect"
func f(a int) string {return fmt.Sprint(a) }
func main() {
    v := reflect.ValueOf(f)
    fmt.Printf("%T\n", v.Interface())
    g := v.Interface().(func(a int)string)
    fmt.Println(g(3))
}

[rsc]

Comment 3:

Here's a concrete example:
func genericSwap(x []reflect.Value) []reflect.Value {
    return []reflect.Value{x[1], x[0]}
}
func MakeSwap(v interface{}) {   // v is a *func(t1, t2)(t2, t1)
    vv := reflect.ValueOf(v).Elem()
    vv.Set(reflect.MakeFunc(v.Type(), genericSwap))
}
and then a caller can write
var f func(int, int) (int, int)
otherpkg.MakeSwap(&f)
println(f(1,2))  // 2, 1
var g func(string, int) (int, string)
otherpkg.MakeSwap(&g)
println(g("hello", 42)) // 42, "hello"
This is a dumb but I hope illustrative example.
The point is that MakeFunc turns a function with a
reflecty type signature into one with a specific
concrete signature, so that you can use it with things
that don't know/care about reflect.
It's for creating Func Values where there wasn't
previously a function.

[bradfitz]

Comment 4:

Rob, I want this for more natural APIs when embedding scripting languages in Go.

[gopherbot]

Comment 5 by m@capitanio.org:

+1 As I see it, that could simplify a lot of my Go code too.

[rsc]

Comment 6:

Labels changed: added priority-later, removed priority-medium.

[rsc]

Comment 8:

Labels changed: added go1.1.

[rsc]

Comment 9:

This issue was closed by revision ba4625c.

Status changed to Fixed.