CODEWITHSUNDEEP
go
Takayuki Sato
Takayuki Sato

Reputation: 1043

Is it possible to know the type of return value of a function in Go?

For example, I want to do something like this,

package main

import (
    "fmt"
    "reflect"
)

func main() {
    var f func(int) int
    v := reflect.ValueOf(f)
    fmt.Println(v.ReturnType() == reflect.TypeOf(1)) // => true
}

ReturnType method doesn't exist in reflect package. My question is, can I implement such a function without using cgo.

Upvotes: 4

Views: 1006

Answers (1)

Linear
Linear

Reputation: 22196

Rather than using reflect.ValueOf(f) try reflect.TypeOf(f). The Type type has two relevant methods named NumOut and Out(int). To get the types of all return values in order, you can use the following loop

typ := reflect.TypeOf(f)

for i := 0; i < typ.NumOut(); i++ {
    returnType := typ.Out(i)
    // do something with returnType
}

If you're certain your function only has one return value, you can always get it with Out(0), the standard disclaimers about making sure your input is correct apply.

Upvotes: 6

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