c++ - 几乎总是 decltype(auto)？

Question

decltype(auto) 可以推导出一个value和一个reference。 auto 从不推断 reference。在我看来，通用代码和优化 decltype(auto) 应该始终是首选。是这样吗？例如，考虑返回一个对象，该对象可能是可复制的，也可能是不可复制的。 auto& 是避免复制它所必需的，但这会强制它始终是一个引用。 decltype(auto) 在这种情况下是正确的选项。 decltype(auto)除了打字多了还有什么缺点？

Answer 1

来自 decltype(auto) 上的 isocpp C++14 常见问题解答:

Note: decltype(auto) is primarily useful for deducing the return type of forwarding functions and similar wrappers, as shown above, where you want the type to exactly “track” some expression you’re invoking. However, decltype(auto) is not intended to be a widely used feature beyond that. In particular, although it can be used to declare local variables, doing that is probably just an antipattern since a local variable’s reference-ness should not depend on the initialization expression. Also, it is sensitive to how you write the return statement. These two functions have different return types. look_up_a_string_1 returns a string while look_up_a_string_2 returns a string&.

decltype(auto) look_up_a_string_1() { auto str = lookup1(); return str; }
decltype(auto) look_up_a_string_2() { auto str = lookup1(); return(str); }