在结构“函数”中使用指针与复制

Question

I'm rather new to Go, and I really can't decide when to use a pointer vs a copy when writing struct "functions" (is that the proper term?)

type Blah struct {
    c complex128
    s string
    f float64
}

func (b * Blah) doPtr() {
    fmt.Println(b.c, b.s, b.f);
}

func (b Blah) doCopy() {
    fmt.Println(b.c, b.s, b.f);
}

Now, my C++ background tells me doPtr is more efficient in both speed and memory, however a lot of examples use doCopy unless you're modifying the object, so am I missing something?

Answer 1

[Go] Frequently Asked Questions (FAQ)

Should I define methods on values or pointers?

For types such as basic types, slices, and small structs, a value receiver is very cheap so unless the semantics of the method requires a pointer, a value receiver is efficient and clear.

For performance issues, don't guess. Run a benchmark. For example,

file: bench_test.go

package main

import (
    "testing"
)

type Blah struct {
    c complex128
    s string
    f float64
}

func (b *Blah) doPtr() {
}

func (b Blah) doCopy() {
}

func BenchmarkDoPtr(b *testing.B) {
    blah := Blah{}
    for i := 0; i < b.N; i++ {
        (&blah).doPtr()
    }
}

func BenchmarkDoCopy(b *testing.B) {
    blah := Blah{}
    for i := 0; i < b.N; i++ {
        blah.doCopy()
    }
}

Output:

$ go test -bench=.
testing: warning: no tests to run
PASS
BenchmarkDoPtr  2000000000           1.26 ns/op
BenchmarkDoCopy 50000000            32.6 ns/op
ok      so/test 4.317s
$