1. 条件编译

Go
GoBuild Constraints
build tag

2. 编译标签

​编译标签是一种通过在源码文件顶部添加注释，来决定文件是否参与编译的约束方式。其格式如下：

// +build <tags>

// +build
// +build linux

// main package comment
package main

Go
tags
ORAND!NOT+build与

标签可以指定为以下内容：

GOOSlinuxdarwinwindowsGOARCHamd64x86i386gcgccgoCGOcgogoGo Version 1.1go1.1Go Version 1.12go1.12
go build -tags

使用示例：

(linux AND 386) OR (darwin AND (NOT cgo))
// +build linux,386 darwin,!cgo


(linux OR darwin) AND amd64
// +build linux darwin

// +build amd64


ignore
// +build ignore


linuxwindows amd64
// +build linux windows,amd64

package main

+build+build
Gininternal/jsonjsonjsonjsoniter
jsoniter.go
// Copyright 2017 Bo-Yi Wu.  All rights reserved.
// Use of this source code is governed by a MIT style
// license that can be found in the LICENSE file.

// +build jsoniter

package json

import "github.com/json-iterator/go"

var (
    json = jsoniter.ConfigCompatibleWithStandardLibrary
    // 通过函数值，Marshal 等函数都由 Gin 下的 json 包导出
    Marshal = json.Marshal
    Unmarshal = json.Unmarshal
    MarshalIndent = json.MarshalIndent
    NewDecoder = json.NewDecoder
    NewEncoder = json.NewEncoder
)

json.go
// Copyright 2017 Bo-Yi Wu.  All rights reserved.
// Use of this source code is governed by a MIT style
// license that can be found in the LICENSE file.

// +build !jsoniter

package json

import "encoding/json"

var (
    // 通过函数值，Marshal 等函数都由 Gin 下的 json 包导出
    Marshal = json.Marshal
    Unmarshal = json.Unmarshal
    MarshalIndent = json.MarshalIndent
    NewDecoder = json.NewDecoder
    NewEncoder = json.NewEncoder
)

Ginencoding/jsonjson
$ go build -tags=jsoniter .

jsoniter.go
$ go build -tags=go_json .

Gin-tags=jsoniterjsoniter.gojsonjsoniterjsonjsonGinjson

3. 文件后缀

除了编译标签，第二种添加编译约束的方法是通过源码文件的文件名实现的，这种方案比构造标签方案更简单。编译器也会根据文件后缀来自动选择编译文件：

$filename_$GOOS.go
$filename_$GOARCH.go
$filename_$GOOS_$GOARCH.go

$filename$GOOS$GOARCH
$filename_$GOOS_$GOARCH.go
os

构建标签和文件名后缀在功能上是重叠的，根据需要选择合适的就行。