std::declval

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Defined in header <utility>

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template <class T>
typename std::add_rvalue_reference<T>::type declval();

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Converts any type T to a reference type, making it possible to use member functions in Template:cpp expressions without specifying constructors. It is commonly used in templates where acceptable template parameters may have no constructor in common, but have the same member function whose return type is needed. Template:cpp can only be used in unevaluated contexts, it is an error to evaluate an expression that contains this function.

Parameters

(none)

Return value

Cannot be called, thus never returns a value, but the return type is T&& unless T is a reference type, in which case T& is returned.

Exceptions

noexcept specification:  

noexcept

  

See also

Template:cpp/keywords/dcl list decltype

result_ofinvoke_result (C++11)(removed in C++20)(C++17)

deduces the result type of invoking a callable object with a set of arguments (class template)