std::experimental:: nullopt_t
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Defined in header
<experimental/optional>
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||
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struct
nullopt_t
;
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(library fundamentals TS) | |
std::experimental::nullopt_t
is an empty class type used to indicate
optional
type with uninitialized state. In particular,
std::
experimental
::
optional
has a constructor with
nullopt_t
as a single argument, which creates an optional that does not contain a value.
std::experimental::nullopt_t
must be a
LiteralType
and cannot have a default constructor.
It must have a
constexpr
constructor that takes some implementation-defined literal type.
Notes
nullopt_t
is not
DefaultConstructible
to support both
op
=
{
}
;
and
op
=
nullopt
;
as the syntax for disengaging an optional object.
A possible implementation of this class is
struct nullopt_t { constexpr nullopt_t(int) {} };
See also
|
(C++17)
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an object of type
nullopt_t
(constant) |