将[] interface {}转换为非可变函数的参数

Question

I am looking for an elegant way to unzip a list of arguments in Go. I do not want to use a variadic function for that purpose because in my usecase when writing a function I already know the number of arguments and I want to keep that part simple. However in my usecase the parameters arrive as []interface{}. I could not find a solution but hey maybe someone out there already knows how to do that?

package main

import (
    "fmt"
)

// NON-VARIADIC greater
func greet(n1, n2 string) {
    fmt.Printf("%s %s
", n1, n2)
}


func main() {
    l := []interface{}{"hello", "world"}

    // works
    greet(l[0].(string), l[1].(string))

    // does not work: "./args.go:20: not enough arguments in call to greet"
    //greet(l...)

    // is there something more elegant to unzip the list?
}

Answer 1

You could create a "generic" caller using reflect package, although this comes with overhead and lacks type safety. Unless you have some special case situation and don't know what you want to call in the code, it would be wiser to use the snippet from your question which works, but you consider not elegant.

Example usage of reflect which could be your starting point:

package main

import (
    "fmt"
    "reflect"
)

func call(f interface{}, args []interface{}) {
    // Convert arguments to reflect.Value
    vs := make([]reflect.Value, len(args))
    for n := range args {
        vs[n] = reflect.ValueOf(args[n])
    }
    // Call it. Note it panics if f is not callable or arguments don't match
    reflect.ValueOf(f).Call(vs)
}

func greet(n1, n2 string) {
    fmt.Printf("%s %s
", n1, n2)
}

func main() {
    l := []interface{}{"hello", "world"}
    call(greet, l)
}

// Output: hello world

https://play.golang.org/p/vbi3CChCdV