go 语言的一个赋值操作

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()
}

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() 
}

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