go build 实现包切换

参考 Gin 的实现

gin 在 internal/json包中实现了多个 json 包的序列化能力, 默认使用官方encoding/json包. 如何保证这些包不会冲突呢?

这里用到了 go build -tags 的能力.

[json.go](https://github.com/gin-gonic/gin/blob/master/internal/json/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.

//go:build !jsoniter && !go_json && !(sonic && avx && (linux || windows || darwin) && amd64)
// +build !jsoniter
// +build !go_json
// +build !sonic !avx !linux,!windows,!darwin !amd64

package json

import "encoding/json"

var (
	// Marshal is exported by gin/json package.
	Marshal = json.Marshal
	// Unmarshal is exported by gin/json package.
	Unmarshal = json.Unmarshal
	// MarshalIndent is exported by gin/json package.
	MarshalIndent = json.MarshalIndent
	// NewDecoder is exported by gin/json package.
	NewDecoder = json.NewDecoder
	// NewEncoder is exported by gin/json package.
	NewEncoder = json.NewEncoder
)

[jsoniter.go](https://github.com/gin-gonic/gin/blob/master/internal/json/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.

//go:build jsoniter
// +build jsoniter

package json

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

var (
	json = jsoniter.ConfigCompatibleWithStandardLibrary
	// Marshal is exported by gin/json package.
	Marshal = json.Marshal
	// Unmarshal is exported by gin/json package.
	Unmarshal = json.Unmarshal
	// MarshalIndent is exported by gin/json package.
	MarshalIndent = json.MarshalIndent
	// NewDecoder is exported by gin/json package.
	NewDecoder = json.NewDecoder
	// NewEncoder is exported by gin/json package.
	NewEncoder = json.NewEncoder
)

切换 不同的 json实现

采用 jsoniter包

go build -tags=jsoniter .

条件编译

通过在代码中增加注释//+build xxx时,编译时传递对应的tags值,就会编译不同的文件.

• 构建约束以一行+build开始的注释.在+build之后列出了一些条件,在这些条件成立时,该文件应包含在编译的包中;
• 约束可以出现在任何源文件中,不限于go文件;
• +build必须出现在package语句之前,+build注释之后应要有一个空行.

参考

-Compile and install the application
-Compile_packages_and_dependencies
-Go条件编译