从函数返回时，auto和decltype(auto)有什么区别吗?

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.

我很少看到decltype(auto)，但当我做它的时候，它会让我感到困惑，因为它在从一个函数返回时似乎也会做同样的事情。

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

What is the difference between these two syntaxes?

这两个语法有什么不同?

2 个解决方案

#1

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

auto遵循模板参数演绎规则，始终是对象类型;decltype(auto)遵循根据值类别推断引用类型的解密规则。如果我们有

int x;
int && f();

then

然后

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

#2

auto returns what value-type would be deduced of you assigned the return clause to an auto variable. decltype(auto) returns what type you would get if you wrapped the return clause in decltype.

自动返回您将返回子句分配给自动变量的值类型。decltype(自动)返回如果你用decltype来包装返回子句，你会得到什么类型。

auto returns by value, decltype maybe not.

自动返回值，解密可能不是。

#1