Go Modules介绍

为了解决Go包管理的问题，Go从1.11开始加入了Go Modules这一新特性。让包的依赖和版本管理更加容易。golang

modulemodulego.modgo.modmoduleimportpathmodule
Go 1.11须要设置GO111MODULE来开启module功能 
GO111MODULE=on，会开启使用module
GO111MODULE=auto默认值，会根据当前目前来决定是否开启module。若是当前目录在``GOPATH/src``以外且当前目录有``go.mod``文件或当前文件在包含go.mod文件的目录下面
从Go 1.13开始module被默认开启

建立一个module

GOPATH/srchellohello.go
package hello

func Hello() string {
    return "Hello, world."
}
hello_test.go
package hello

import "testing"

func TestHello(t *testing.T) {
    want := "Hello, world."
    if got := Hello(); got != want {
        t.Errorf("Hello() = %q, want %q", got, want)
    }
}

运行go test命令，这个时候返回：get

PS D:\Code\hello> go test
PASS
ok      _/D_/Code/hello 0.176s
D:\Code\helloGOPATH/src_/D_/Code/hello
go mod init 
go mod init example.com/hello
go: creating new go.mod: module example.com/hello

go test
PASS
ok      example.com/hello       0.177s
ok example.com/hello 0.177sgo.mod
module example.com/hello

go 1.14
modmoduleimport pathpath

添加外部依赖

在hello.go文件中导入一个外部的包：io

package hello

import "rsc.io/quote"

func Hello() string {
    return quote.Hello()
}

运行单测：

go: finding module for package rsc.io/quote
go: found rsc.io/quote in rsc.io/quote v1.5.2
--- FAIL: TestHello (0.00s)
    hello_test.go:8: Hello() = "你好，世界。", want "Hello, world."
PASS
ok      example.com/hello       0.177s
go.mod
module example.com/hello

go 1.14

require rsc.io/quote v1.5.2
rsc.io/quotego.mod
PASS
ok      example.com/hello       0.177s
gorsc.io/quotego list -m all 
example.com/hello
golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c
rsc.io/quote v1.5.2
rsc.io/sampler v1.3.0
rsc.io/quotego.modgo.sum
golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c h1:qgOY6WgZOaTkIIMiVjBQcw93ERBE4m30iBm00nkL0i8=
golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
rsc.io/quote v1.5.2 h1:w5fcysjrx7yqtD/aO+QwRjYZOKnaM9Uh2b40tElTs3Y=
rsc.io/quote v1.5.2/go.mod h1:LzX7hefJvL54yjefDEDHNONDjII0t9xZLPXsUe+TKr0=
rsc.io/sampler v1.3.0 h1:7uVkIFmeBqHfdjD+gZwtXXI+RODJ2Wc4O7MPEh/QiW4=
rsc.io/sampler v1.3.0/go.mod h1:T1hPZKmBbMNahiBKFy5HrXp6adAjACjK9JXDnKaTXpA=

后面增长了每一个外部依赖内容的hash值，go经过这些hash值去验证你下载依赖的正确性。

升级版本

go list -m allgolang.org/x/text v0.0.0-20170915032832-14c0d48ead0cv0.0.0-20170915032832-14c0d48ead0c
go get golang.org/x/text
go: golang.org/x/text upgrade => v0.3.3
go: downloading golang.org/x/text v0.3.3

go test
PASS
ok      example.com/hello       0.199s
go.mod
module example.com/hello

go 1.14

require (
	golang.org/x/text v0.3.3 // indirect
	rsc.io/quote v1.5.2
)
golang.org/x/text v0.3.3 // indirectv0.3.3
go list -m all 
example.com/hello
golang.org/x/text v0.3.3
golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e
rsc.io/quote v1.5.2
rsc.io/sampler v1.3.0

移除没有使用的依赖

go mod tidy

下载依赖到当前目录

go mod vendor

老项目的迁移

GOPATH/src
go mod init xxx

go build

须要注意的是迁移项目可能会出现包冲突的问题，会报相似

cannot load xxxx: ambiguous import: found xxxx in multiple modules:

这样的错误，这时可能须要再go.mod中手动指定这个包的版本号