go 语言的一个赋值操作

Posted 2022-01-08 charlieroro

 最近在看client-go源码，在源码的\tools\caches\store.go文件中有一行代码不得其解(如下标黄内容)，它将一个struct赋值给了一个interface

type Store interface 
    Add(obj interface) error
    Update(obj interface) error
    Delete(obj interface) error
    List() []interface
    ListKeys() []string
    Get(obj interface) (item interface, exists bool, err error)
    GetByKey(key string) (item interface, exists bool, err error)

    // Replace will delete the contents of the store, using instead the
    // given list. Store takes ownership of the list, you should not reference
    // it after calling this function.
    Replace([]interface, string) error
    Resync() error


type cache struct 
    // cacheStorage bears the burden of thread safety for the cache
    cacheStorage ThreadSafeStore
    // keyFunc is used to make the key for objects stored in and retrieved from items, and
    // should be deterministic.
    keyFunc KeyFunc


var _ Store = &cache

google搜索后没有得到结果，在stackoverflow上提交了一个问题golang syntax in client-go，很快就得到了回答(老外自由时间果然比较多^^)，“var _ Store = &cache”的作用是强制要求cache结构实现Store接口。

做个测试，TestSt实现了TestIf接口中的一个方法write，但由于没有实现read，则其并没有实现TestIf接口

下述代码是可以运行的

package main

import "fmt"

type TestIf interface 
    write(w string)
    read()


type TestSt struct 



func (t *TestSt)write(w string)
    fmt.Println("write")


func main() 
    fmt.Println(111)

但下述是不可以运行的

package main

import "fmt"

type TestIf interface 
    write(w string)
    read()


type TestSt struct 



func (t *TestSt)write(w string)
    fmt.Println("write")


var _ TestIf=&TestSt

func main()  
    fmt.Println(111) 

报出的错误如下：

Cannot use ‘&TestSt‘ (type *TestSt) as type TestIf in assignment Type does not implement ‘TestIf‘ as some methods are missing: read() more... (Ctrl+F1)

该语法实际就是实现了某结构必须实现某接口的强制要求