最烦恼的解析与合格的id - 或不？ [英] Most vexing parse with a qualified-id - or not?

问题描述

请考虑：

struct Foo {
     enum { bar };
     explicit Foo(int){}
};

struct Baz { explicit Baz(Foo){} };

Baz b(Foo(Foo::bar)); // #1

行＃1是最烦琐的解析，即使 Foo :: bar 是一个 qualified-id ，不能是有效的参数名称？ Clang和GCC不同意;哪个编译器是正确的？

Is line #1 the most vexing parse, even though Foo::bar is a qualified-id and can't possibly be a valid parameter name? Clang and GCC disagree; which compiler is correct?

推荐答案

Clang是对的。

令人惊讶的是，参数声明的语法允许限定符和非限定id ，因为它接受所有声明符 s：

Somewhat surprisingly, the grammar for parameter-declaration permits both qualified- and unqualified-ids, because it accepts all declarators:

parameter-declaration:
    attribute-specifier-seq_opt decl-specifier-seq declarator
    attribute-specifier-seq_opt decl-specifier-seq declarator = initializer-clause
    attribute-specifier-seq_opt decl-specifier-seq abstract-declarator_opt
    attribute-specifier-seq_opt decl-specifier-seq abstract-declarator_opt = initializer-clause

并且声明器的语法允许合格 - 和非限定id 。对于函数参数名称的无 qualified-id 规则，无论更好还是更差，都是语义规则，即使可以很容易地为参数声明直接排除 qualified-id 。

and the grammar for a declarator permits both qualified- and unqualified-ids. The "no qualified-id for function parameter names" rule, for better or worse, is a semantic rule, even though it is easily possible to write a grammar for parameter-declaration that excludes qualified-ids directly.

就像这个问题，消歧规则是纯粹的句法，因为

Just like the situation in this question, the disambiguation rule is purely syntatic, and since

Baz b(Foo(Foo::bar));

可以作为函数声明进行语法分析，因此它被解析，即使这种情况下的消歧

can syntatically be parsed as a function declaration, it is so parsed, even though the disambiguation in this case results in something that can never compile.

另请参阅 clang bug 4594 。

这篇关于最烦恼的解析与合格的id - 或不？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！