Now that we're using C++17, we can use the decltype(auto) return type
(available since C++14) for functions and lambda expressions.
As demonstrated in this commit, this can simplify cases where previously
the compiler failed to deduce the correct return type.
Just for reference, for the "assign to ref" cases fixed here, there are
3 possible solutions:
- Return a pointer and immediately deref as used before this commit
- Make sure the function/lambda returns declspec(auto) as used after
this commit
- Class& i = WITH_LOCK(..., return std::ref(...));
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References:
1. https://en.cppreference.com/w/cpp/language/function#Return_type_deduction
2. https://en.cppreference.com/w/cpp/language/template_argument_deduction#Other_contexts
3. https://en.cppreference.com/w/cpp/language/auto
4. https://en.cppreference.com/w/cpp/language/decltype
Explanations:
1. https://stackoverflow.com/a/21369192
2. https://stackoverflow.com/a/21369170
3. Item 3 in Effective Modern C++ (Scott Meyers) via jnewbery
This is a backport of core#20495
Depends on D14641