可变参数打包并解压到go lang：“ [] string {f（v）}…”

Question

I found this function while browsing github:

func Accumulate(s []string, f func(st string) string) (result []string) {
    for _, v := range s {
        result = append(result, []string{f(v)}...)
    }
    return result
}

Could this method be simplified to the following, or am I missing something:

func Accumulate(s []string, f func(st string) string) (result []string) {
    for _, v := range s {
        result = append(result, f(v))
    }
    return result
}

Answer 1

The version you have written is correct and sane to understand. I wrote a benchmark:

package p

import (
    "testing"
    "strings"
)

var s = []string{"hello", "world", "this", "new", "world"}

func BenchmarkAcc1(b *testing.B) {
    for n := 0; n < b.N; n++ {
        Accumulate(s, strings.ToUpper)
    }
}

func BenchmarkAcc2(b *testing.B) {
    for n := 0; n < b.N; n++ {
        Accumulate2(s, strings.ToUpper)
    }
}

Here are a few results I got:

% go test -benchtime=10s -bench=.
testing: warning: no tests to run
PASS
BenchmarkAcc1   10000000          1510 ns/op
BenchmarkAcc2   10000000          1492 ns/op
ok      _/home/satran/test  33.064s

As you can see there is no performance gain either, in fact your version works better.

Here is the source:

package p

func Accumulate(s []string, f func(st string) string) (result []string) {
    for _, v := range s {
        result = append(result, []string{f(v)}...)
    }
    return result
}

func Accumulate2(s []string, f func(st string) string) (result []string) {
    for _, v := range s {
        result = append(result, f(v))
    }
    return result
}