hof_test.go

/*

go test -bench=. -test.benchmem=true -test.benchtime=10s

goos: darwin
goarch: amd64

BenchmarkDirectCall-12    	1000000000	         1.31 ns/op	       0 B/op	       0 allocs/op
BenchmarkInterface-12     	1000000000	         1.69 ns/op	       0 B/op	       0 allocs/op
BenchmarkHoF-12           	1000000000	         1.61 ns/op	       0 B/op	       0 allocs/op

*/
package hof_test

import (
	"testing"
)

type Foo struct {
	a int
}

type Handler interface {
	Serve(x int)
}

type HoF func(x int)

func (foo *Foo) Serve(x int) {
	foo.a = foo.a + x
}

func FooHoF(foo *Foo) HoF {
	return func(x int) {
		foo.a = foo.a + x
	}
}

var result Handler

func BenchmarkDirectCall(b *testing.B) {
	f := &Foo{}
	for n := 0; n < b.N; n++ {
		f.Serve(n)
	}
	result = f
}

func BenchmarkInterface(b *testing.B) {
	var f Handler
	f = &Foo{}
	for n := 0; n < b.N; n++ {
		f.Serve(n)
	}
	result = f
}

func BenchmarkHoF(b *testing.B) {
	f := &Foo{}
	hof := FooHoF(f)
	for n := 0; n < b.N; n++ {
		hof(n)
	}
	result = f
}

In BenchmarkInterface, you did not call (*Foo).Serve via the Handler interface. It's a direct function call.

Yeah, thanks for notice this! Just updated.