为什么“auto”声明都是相同类型？ [英] Why must 'auto' declarations all be of the same type?

问题描述

似乎不允许使用 auto 关键字声明不同类型的多个变量。

It appears that it is not allowed to declare multiple variables of distinct types using the auto keyword. I can't figure out the wording in the standard that would prevent it however.

auto i = 1, j = 1.0; //deduction failure (several compilers)

历史上我明白，因为你只有一个< specifier-spec 。然而，标准中的规则似乎并不排除，事实上他们鼓励， auto 可以是每个的不同类型。考虑这些段落：

Historically I understand since you have only one decl-specifier-spec. However, the rules in the standard don't seem to preclude, in fact they encourage, that auto can be a distinct type for each. Consider these paragraphs:

8-3每个声明中的 init-declarator

7.1.6.4-7如果声明器列表包含多个声明器，则每个声明变量的类型被确定为
as如上所述。 [...]

7.1.6.4-7 If the list of declarators contains more than one declarator, the type of each declared variable is determined as described above. [...]

即使没有 auto ，相同类型，因为某些修饰符如 * 可以单独应用于每个声明器。对我来说，现在看来，该措辞允许每个 auto 声明符是一个完全不同的类型。

Even without auto not all variables needed to have the same type, as certain modifiers like * could be applied to each declarator individually. To me it appears now that the wording allows each auto declarator to be a completely distinct type.

禁止此操作？

推荐答案

类型扣除对列表中的每个对象执行，但最终结果必须是单个类型 [dcl.spec.auto] / 7 （强调我的）：

Type deduction is performed for every object in the list, but the final result must be a single type [dcl.spec.auto]/7 (emphasis mine):

的声明符包含多个声明符，每个声明变量的类型如上所述确定。 如果在每次扣减中，对于模板参数U推导的类型不相同，则该程序不成立。

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