英文:
Struct in for loop initializer
问题
有没有想法为什么这个在for循环初始化器中的结构表达式会在编译时出现语法错误？在这种情况下，指向结构体的指针可以正常工作，但是我当然需要像下面这样的局部变量。谢谢建议！
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
}
}()
英文:
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
}
}()
答案1
得分: 20
简化你的代码：
for r := Request{}; r.err == nil; r.id++ {
r.line, r.err = input.ReadSlice(0x0a)
channel <- r
}
会产生编译时错误：
预期布尔值或范围表达式，找到简单语句（缺少复合字面量周围的括号？）（还有1个错误）
这个结构在解析时是有歧义的。开括号'{'不明显是一个复合字面量的一部分，还是for语句本身（for块）的开括号。
你可以通过在复合字面量周围使用括号（如错误建议所示）来明确表示：
for r := (Request{}); r.err == nil; r.id++ {
r.line, r.err = input.ReadSlice(0x0a)
channel <- r
}
英文:
Simplifying you code:
for r := Request{}; r.err == nil; r.id++ {
r.line, r.err = input.ReadSlice(0x0a)
channel <- r
}
Gives compile time error:
> expected boolean or range expression, found simple statement (missing parentheses around composite literal?) (and 1 more errors)
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).
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
}
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