c++ - 为什么 'auto' 声明都必须是同一类型？

Question

似乎不允许使用 auto 关键字声明多个不同类型的变量。但是，我无法弄清楚标准中会阻止它的措辞。

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

从历史上看，我理解，因为您只有一个 decl-specifier-spec。然而，标准中的规则似乎并没有排除，事实上它们鼓励 auto 可以是每个不同的类型。考虑以下段落:

8-3 Each init-declarator in a declaration is analyzed separately as if it was in a declaration by itself.

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 也不是所有变量都需要具有相同的类型，因为像 * 这样的某些修饰符可以单独应用于每个声明符。在我看来，现在的措辞允许每个 auto 声明符是完全不同的类型。

哪一段会禁止这样做？

Answer 1

对列表中的每个对象进行类型推导，但最终结果必须是单一类型 [dcl.spec.auto]/7(强调我的):

If the list of declarators contains more than one declarator, the type of each declared variable is determined as described above. If the type deduced for the template parameter U is not the same in each deduction, the program is ill-formed.