Talk:cpp/language/decltype

For the following function, the function body is missing:

auto add(T t, U u) -> decltype(t + u); // return type depends on template parameters

if someone tries to run the code (as is) by calling add(), it will generate a compiler error.

It should have the following body: auto add(T t, U u) -> decltype(t + u) // return type depends on template parameters {

  return t+u;

}

Shimon0505004 (talk) 13:52, 1 June 2017 (PDT)

With a definition, the decltype becomes redundant since that return is deducible: it was there demonstrating the use in a declaration. But it's not technically wrong either way. --Cubbi (talk) 14:44, 1 June 2017 (PDT)

Parens and auto

Can we expand this page to clarify a few cases in particular?:

• decltype(auto) is important as it's the perfect-forwarding return type.
• We mention it, but the distinction between decltype((x)) and decltype(x) really isn't clear and could do with examples. It appears that if I have int i; then decltype(i) is int and decltype((i)) is int&.
• Even with decltype((x)), I believe there's a common use for std::decay_t<decltype(x)>, such as [](auto&& x) { using T = std::decay_t<decltype(x)>; ... } to get the plain old type of x without any const or reference qualification.

BenFrantzDale (talk) 10:09, 7 September 2021 (PDT)

Wrong References

According to:

• C++17 standard (ISO/IEC 14882:2017)
• C++14 standard (ISO/IEC 14882:2014)
• C++11 standard (ISO/IEC 14882:2011)

id dcl.type.decltype is absent in: (C++11), (C++14) and (C++17).

Section References should be corrected.

Best regards, Benio (talk) 22:04, 13 August 2024 (PDT)