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std::experi...al::value_or(3)  C++ Standard Libary std::experi...al::value_or(3)

NAME
     std::experimental::optional::value_or	  -	  std::experimental::op-
     tional::value_or

Synopsis
	template< class U >				   (library fundamentals
     TS)
	constexpr T value_or( U&& default_value ) const&;
	template< class U >				   (library fundamentals
     TS)
	constexpr T value_or( U&& default_value ) &&;

	Returns the contained value if *this has a value, otherwise returns  de-
     fault_value.

	1) Equivalent to bool(*this) ? **this :
	static_cast<T>(std::forward<U>(default_value)).
	2) Equivalent to bool(*this) ? std::move(**this) :
	static_cast<T>(std::forward<U>(default_value)).

Parameters
	default_value	      - 	the value to use in case *this is empty

Type requirements
	-
	T  must meet the requirements of CopyConstructible in order to use over-
     load (1).
	-
	T must meet the requirements of MoveConstructible in order to use  over-
     load (2).
	-
	U&& must be convertible to T.

Return value
	The current value if *this has a value, or default_value otherwise.

Exceptions
	Any exception thrown by the selected constructor of the return value T.

Example
     // Run this code

      #include <cstdlib>
      #include <experimental/optional>
      #include <iostream>

      std::experimental::optional<const char*> maybe_getenv(const char* n)
      {
	  if (const char* x = std::getenv(n))
	      return x;
	  else
	      return {};
      }

      int main()
      {
	  std::cout << maybe_getenv("MYPWD").value_or("(none)") << '\n';
      }

Possible output:
      (none)

See also
	value returns the contained value
	      (public member function)

Category:
	  * Noindexed pages

http://cppreference.com 	   2024.06.10	   std::experi...al::value_or(3)
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