从函数返回时，auto和decltype（auto）有什么区别？ [英] What is the difference between auto and decltype(auto) when returning from a function?

问题描述

我很少看到 decltype（auto），但是当我这样做时，我感到困惑，因为它似乎和 auto 。

I rarely see decltype(auto) but when I do it confuses me because it seems to do the same thing as auto when returning from a function.

auto g() { return expr; }
decltype(auto) g() { return expr; }

这两种语法有什么区别？

What is the difference between these two syntaxes?

推荐答案

auto 遵循模板参数推导规则，并且始终是对象类型； decltype（auto）遵循 decltype 规则，用于基于值类别推导引用类型。因此，如果我们有

auto follows the template argument deduction rules and is always an object type; decltype(auto) follows the decltype rules for deducing reference types based on value categories. So if we have

int x;
int && f();

然后

expression    auto       decltype(auto)
----------------------------------------
10            int        int
x             int        int
(x)           int        int &
f()           int        int &&

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