Golang Modules

Create a new module

stay $GOPATH/src Folder outside （ such as //hello）, Create a new go file , for instance hello.go. And let's write him a test. It will be found after running

PASS
ok _/hello

Because we work in $GOPATH And any module outside ,go The command does not know the import path of the current directory （ The import path is the only string ID that identifies the package ） So a fake import path is created according to the location of the directory _/hello

Let's use go mod init Initialize the folder to module Well ！

go mod init demo.com/hello

go mod init Will write go.mod file

go.mod It will only appear in the root directory of the module . The subdirectory package import path under the module consists of the module path plus the subdirectory path . For example, there are subdirectories under the module /world, Then the import path is demo.com/hello/world

Add dependency

go Command by using go.mod Specific dependent module versions are listed in to resolve the import . When go.mod Unspecified time , Will automatically find the latest dependency , Add to go.mod

Except, of course, go.mod Beyond the direct dependencies listed in , There are also some indirect dependencies . for instance rsc.io/quote This module also relies on rsc.io/sampler, that rsc.io/sampler Will also download

It can be done by go list -m all List all dependencies of the current module

Besides ,go.sum Also record encrypted hash values that depend on the module version . but go.sum Not at all package-lock.json, Only all direct and indirect dependencies of the current module will be recorded , And checksums .

Upgrade dependency

We can go through go get To upgrade to the latest dependent version .

But sometimes there are incompatibilities

$ go get rsc.io/sampler
go: finding rsc.io/sampler v1.99.99
go: downloading rsc.io/sampler v1.99.99
go: extracting rsc.io/sampler v1.99.99
$ go test
--- FAIL: TestHello (0.00s)
    hello_test.go:8: Hello() = "99 bottles of beer on the wall, 99 bottles of beer, ...", want "Hello, world."
FAIL
exit status 1
FAIL    example.com/hello   0.014s
$

At this point, you can list all modules available tagged edition , Then select a compatible version to download

$ go list -m -versions rsc.io/sampler
rsc.io/sampler v1.0.0 v1.2.0 v1.2.1 v1.3.0 v1.3.1 v1.99.99

$ go get rsc.io/[email protected]

Delete dependency

go mod tidy Will clear these unused dependencies

Add dependent major version

Suppose we want to use multiple different master versions of a dependency

package hello

import (
    "rsc.io/quote"
    quoteV3 "rsc.io/quote/v3"
)

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

func Proverb() string {
    
    return quoteV3.Concurrency()
}

Go Each different version of the module uses a different module path .

replace Replace require Declaration of dependency

module demo

replace outter => /local/outter

require (
			outter v1.0.0
)

Ref

1. https://go.dev/blog/using-go-modules
2. https://thewebivore.com/using-replace-in-go-mod-to-point-to-your-local-module/