Tendermint源码阅读（五）

关注点：go语言的语法技巧

一、问题

看tendermint源码的时候，会经常看见类似下面的代码

var _ types.Application = (*PersistentKVStoreApplication)(nil)

从语义上来说，这句代码的作用强制转换一个空指针到一个unused的变量。这样看来，完全是没什么卵用，那为什么还出现在多个文件里呢？百思不得其解

刚开始不懂，后来慢慢想，猜测是肯定是和编译器相关。

今天浏览后缀是pb.go的源文件时，也发现很多类似的代码

const _ = proto.GoGoProtoPackageIsVersion2

幸运的是，这里有一些注释来解释这个事情

// This is a compile-time assertion to ensure that this generated file
// is compatible with the proto package it is being compiled against.
// A compilation error at this line likely means your copy of the
// proto package needs to be updated.

再去网上查就比较容易了，下面是在Google中搜索到的内容

This post is about a little-known way to make compile-time assertions in Go. You probably shouldn’t use it, but it is interesting to know about.

As a warm-up, here’s a fairly well-known form of compile-time assertions in Go: Interface satisfaction checks.

In this code (playground), the var _ = line ensures that type W is a stringWriter, as checked for by io.WriteString.

详情请查看原文