Function get
boost::get —
Retrieves a value of a specified type from a given
variant.
Synopsis
template<typename U, typename T1, typename T2, ..., typename TN>
U * get(variant<T1, T2, ..., TN> * operand);
template<typename U, typename T1, typename T2, ..., typename TN>
const U * get(const variant<T1, T2, ..., TN> * operand);
template<typename U, typename T1, typename T2, ..., typename TN>
U & get(variant<T1, T2, ..., TN> & operand);
template<typename U, typename T1, typename T2, ..., typename TN>
const U & get(const variant<T1, T2, ..., TN> & operand);
Description
The get function allows run-time checked,
type-safe retrieval of the content of the given
variant. The function succeeds
only if the content is of the specified type U, with
failure indicated as described below.
Warning: After either
operand or its content is destroyed (e.g., when the
given variant is assigned a
value of different type), the returned reference is invalidated.
Thus, significant care and caution must be extended when handling
the returned reference.
|
Notes: |
As part of its guarantee of type-safety, get
enforces const-correctness. Thus, the specified type
U must be const-qualified whenever
operand or its content is likewise
const-qualified. The converse, however, is not required:
that is, the specified type U may be
const-qualified even when operand and its
content are not. |
|
Returns: |
If passed a pointer, get returns a pointer to
the value content if it is of the specified type U;
otherwise, a null pointer is returned. If passed a reference,
get returns a reference to the value content if it is of
the specified type U; otherwise, an exception is thrown
(see below). |
|
Throws: |
Overloads taking a
variant pointer will not
throw; the overloads taking a
variant reference throw
bad_get if the content is not of
the specified type U. |
|
Rationale: |
While visitation via
apply_visitor
is generally preferred due to its greater safety, get may
may be more convenient in some cases due to its straightforward
usage. |
