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The std::declval Type Operator

Explore the std::declval type operator and how it aids in compile-time type deduction in C++ templates. Understand its usage in unevaluated contexts to work with types lacking accessible constructors, enabling versatile template metaprogramming techniques.

The std::declval is a utility type operation function, available in the <utility> header. It’s in the same category as functions such as std::move and std::forward that we have already seen. What it does is very simple: it adds an rvalue reference to its type template argument. The declaration of this function looks as ... ...