std::experimental::optional<T>::value_or

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

Returns the contained value if *this has a value, otherwise returns default_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 overload (1).
-
T must meet the requirements of MoveConstructible in order to use overload (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

#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

 returns the contained value
(public member function)