Go: function declaration vs var (benchmark)

func_decl_test.go

package main

import "testing"

func sum1(a, b int) int {
	return a + b
}

func BenchmarkDefaultDeclaration(b *testing.B) {
	for i := 0; i < b.N; i++ {
		sum1(i, i)
	}
}

func BenchmarkVarDeclaration1(b *testing.B) {
	for i := 0; i < b.N; i++ {
		var sum2 = func(a, b int) int {
			return a + b
		}
		sum2(i, i)
	}
}

func BenchmarkVarDeclaration2(b *testing.B) {
	var sum3 = func(a, b int) int {
		return a + b
	}
	for i := 0; i < b.N; i++ {
		sum3(i, i)
	}
}

var sum4 = func(a, b int) int {
	return a + b
}

func BenchmarkVarDeclaration3(b *testing.B) {
	for i := 0; i < b.N; i++ {
		sum4(i, i)
	}
}

results.txt

goos: linux
goarch: amd64
BenchmarkDefaultDeclaration-8   	1000000000	         0.258 ns/op	       0 B/op	       0 allocs/op
BenchmarkVarDeclaration1-8      	1000000000	         0.256 ns/op	       0 B/op	       0 allocs/op
BenchmarkVarDeclaration2-8      	1000000000	         0.259 ns/op	       0 B/op	       0 allocs/op
BenchmarkVarDeclaration3-8      	706787652	         1.71 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	_/home/kiriost/dev/tmp	2.237s
Success: Benchmarks passed.

If function is declared outside using var it takes more time.