copy
template<
typename Sequence
, typename State
, typename BinaryOp
>
struct copy
{
typedef unspecified type;
};
copy is, in fact, just another name for fold. It was introduced for symmetry with copy_if [1], and because it's a nice name for one of the typical fold applications, that is, copying the content of one sequence into another - see the example below.
#include "boost/mpl/copy.hpp"
| Parameter | Requirement | Description |
|---|---|---|
Sequence | A model of Sequence | A sequence to iterate. |
State | A type | The initial state for the first BinaryOp application. |
BinaryOp | A model of [Lambda Function] | The operation to be executed on forward traversal. |
| Expression | Expression type | Precondition | Semantics | Postcondition |
|---|---|---|---|---|
typedef copy<Sequence,T,Op>::type s; | A type | Equivalent to typedef fold< Sequence,T,Op >::type s;. |
Linear. Exactly size<Sequence>::type::value applications of BinaryOp.
typedef vector_c<int,0,1,2,3,4,5,6,7,8,9> numbers;
typedef copy<
range_c<int,10,20>
, push_back<_,_>
, numbers
>::type result;
BOOST_STATIC_ASSERT(size<result>::value == 20);
BOOST_STATIC_ASSERT((equal< result,range_c<int,0,20> >::type::value));
[1] In case if you wonder why copy_if, in its turn, wasn't just called fold_if, - something that would allow to eliminate the family of copy algorithms completely - these two have quite different semantics.
Algorithms, copy_if, copy_backward, copy_backward_if, fold, fold_backward