NAME¶

std::experimental::optional::value_or - std::experimental::optional::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 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¶

// 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