构造 for 循环初始化程序 [英] Struct in for loop initializer

问题描述

知道为什么 for 循环初始值设定项中的这个结构表达式会在编译时出现语法错误吗?在这种情况下，指向 struct 的指针工作正常，但我需要像波纹管这样的局部变量.谢谢指教！

Any idea why this struct expression in for loop initializer makes syntax error in compile-time? Pointer to struct works fine in this case but ofc I need local variable like bellow. Thanks for advices!

type Request struct {
    id   int
    line []byte
    err  error
}

go func() {
    for r := Request{}; r.err == nil; r.id++ {
        r.line, r.err = input.ReadSlice(0x0a)
        channel <- r
    }
}()

推荐答案

简化代码:

for r := Request{}; r.err == nil; r.id++ {
    r.line, r.err = input.ReadSlice(0x0a)
    channel <- r
}

给出编译时错误:

预期的布尔值或范围表达式，找到简单的语句(复合文字周围缺少括号?)(还有 1 个错误)

expected boolean or range expression, found simple statement (missing parentheses around composite literal?) (and 1 more errors)

这个结构不利于解析.左大括号 '{' 不明显，它是 复合文字 的一部分还是for 语句本身的左大括号(for 块).

This construct is ambiguous to parse. The opening brace '{' is not obvious whether it is part of a composite literal or the opening brace of the for statement itself (the for block).

您可以通过在复合文字周围使用括号来使其显而易见(如错误所示):

You can make it obvious by using parentheses around the composite literal (as the error suggests):

for r := (Request{}); r.err == nil; r.id++ {
    r.line, r.err = input.ReadSlice(0x0a)
    channel <- r
}

这篇关于构造 for 循环初始化程序的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！