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.
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We'll cover the following...
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— ...