The std::declval Type Operator
Discover the capabilities and usage of the std::declval type operator in C++ metaprogramming.
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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 follows:
template<class T>typename std::add_rvalue_reference<T>::type declval() noexcept;
Declaration of declval function
This function has no definition, and therefore, it can’t be called directly. It can only be used in unevaluated contexts— ...