为什么允许使用类型别名作为变量名? [英] Why type alias is allowed as name of variable?

问题描述

什么规则使以下代码编译没有错误:

using integer = int;

struct Foo
{
    int integer;
};

int main() {
    Foo f;
    int integer;
    f.integer;
}

使用当然不是 #define integer int 的简单替代，但是是什么使该代码在 int int;看来显然格式良好?会导致格式错误?

using is of course not a simple replacement for #define integer int, but what makes this code apparently well-formed while int int; would make it ill-formed?

推荐答案

虽然可以访问在外部作用域中声明的名称，然后隐藏该名称，这有点令人惊讶，但这只是规则的直接应用范围:

While it's a little surprising that one can access a name declared in an outer scope, and then later hide that name , it's just a straightforward application of the rules for scoping:

在块(9.3)中声明的名称是该块的本地名称；它具有块范围.它的潜在范围始于其声明点(6.3.2)，并在其块末尾结束.[basic.scope.block]

A name declared in a block (9.3) is local to that block; it has block scope. Its potential scope begins at its point of declaration (6.3.2) and ends at the end of its block. [basic.scope.block]

反过来，名称声明的重点是:

In turn, the point of a name's declaration is:

紧随其完整的声明者(第11条)之后，初始化程序(如果有的话)... [basic.scope.pdecl]

immediately after its complete declarator (Clause 11) and before its initializer (if any)... [basic.scope.pdecl]

因此，当您执行 integerinteger 时，您尚未声明块作用域名称 integer ，这意味着您仍然可以看到全局的 integer .这也意味着您不能执行整数integer integer =(integer)0 .

So when you do integer integer, you haven't yet declared the block-scoped name integer, which means you can still see the global integer. This also means you cannot do integer integer = (integer)0.

更容易解释为什么 int int 无法编译. int 是关键字，因此没有句法规则可以将其声明为名称.它与名称看起来像"的规则不匹配.

It's easier to explain why int int won't compile. int is a keyword, so no syntactic rule which could declare it as a name would be able to; it doesn't match the rules for "what a name looks like".

有五种令牌:标识符，关键字，文字，运算符和其他分隔符.[lex.token]

There are five kinds of tokens: identifiers, keywords, literals, operators, and other separators. [lex.token]

因为 int 是关键字，所以不能是标识符，这意味着它不能是名称.

Because int is a keyword, it cannot be an identifier, which means it cannot be a name.

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