deferが不要な時に使わないことによるメリットをベンチマーク

0result.md

$ go test -bench=.
goos: windows
goarch: amd64
pkg: gist.github.com/koron/bennchdefer
cpu: Intel(R) Core(TM) i9-9900K CPU @ 3.60GHz
BenchmarkWithDefer-16           361817953                3.300 ns/op
BenchmarkWithoutDefer-16        1000000000               0.8443 ns/op
PASS
ok      gist.github.com/koron/bennchdefer    2.650s

defer.go

package benchdefer

var withResult = 0

func WithDefer(a, b int) {
	withResult = 0
	defer func() { withResult *= b }()
	withResult += a
}

var withoutResult = 0

func WithoutDefer(a, b int) {
	withoutResult = 0
	withoutResult += a
	func() { withoutResult *= b }()
}

defer_test.go

package benchdefer

import "testing"

func run(a, b int) (int, int) {
	WithDefer(a, b)
	WithoutDefer(a, b)
	return withResult, withoutResult
}

func TestBasic(t *testing.T) {
	for i := 1; i < 1000; i++ {
		for j := 1; j < 1000; j++ {
			with, without := run(i, j)
			if with != without {
				t.Fatalf("unmatch results for %d,%d: with=%d without=%d", i, j, with, without)
			}
		}
	}
}

func BenchmarkWithDefer(b *testing.B) {
	for i := 0; i < b.N; i++ {
		WithDefer(i/1000, i%1000)
	}
}

func BenchmarkWithoutDefer(b *testing.B) {
	for i := 0; i < b.N; i++ {
		WithoutDefer(i/1000, i%1000)
	}
}

go.mod

module gist.github.com/koron/bennchdefer

go 1.19