关键字 var 后的下划线和接口名称是什么意思? [英] What does an underscore and interface name after keyword var mean?

问题描述

来自 http://golang.org/src/pkg/database/sql/driver/types.go:

type ValueConverter interface {
    // ConvertValue converts a value to a driver Value.
    ConvertValue(v interface{}) (Value, error)
}

var Bool boolType

type boolType struct{}

var _ ValueConverter = boolType{} // line 58

func (boolType) String() string { return "Bool" }

func (boolType) ConvertValue(src interface{}) (Value, error) {....}

我知道 ValueConverter 是一个接口名称.第 58 行似乎声明了 boolType 实现了接口 ValueConverter，但这有必要吗?我删除了第 58 行，代码运行良好.

I known that ValueConverter is an interface name. Line 58 seems to declare that boolType implement interface ValueConverter, but is that necessary? I deleted line 58 and the code works well.

推荐答案

它提供了一个静态(编译时)检查 boolType 是否满足 ValueConverter 接口.用作变量名称的 _ 告诉编译器有效地丢弃 RHS 值，但对其进行类型检查并评估它是否有任何副作用，但匿名变量本身并没有不占用任何进程空间.

It provides a static (compile time) check that boolType satisfies the ValueConverter interface. The _ used as a name of the variable tells the compiler to effectively discard the RHS value, but to type-check it and evaluate it if it has any side effects, but the anonymous variable per se doesn't take any process space.

在开发和接口的方法集和/或类型实现的方法经常更改时，这是一个方便的构造.该构造可防止忘记匹配旨在使它们兼容的类型和接口的方法集.它有效地防止了去安装一个有这种遗漏的损坏(中间)版本.

It is a handy construct when developing and the method set of an interface and/or the methods implemented by a type are frequently changed. The construct serves as a guard against forgetting to match the method sets of a type and of an interface where the intent is to have them compatible. It effectively prevents to go install a broken (intermediate) version with such omission.

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