iter_fold

Synopsis

template<
      typename Sequence
    , typename State
    , typename ForwardOp
    >
struct iter_fold
{
    typedef unspecified type;
};

Returns the result of the successive application of binary ForwardOp to the result of the previous ForwardOp invocation (State if it's the first call) and each iterator in the range [begin<Sequence>::type, end<Sequence>::type) in order.

Header

#include <boost/mpl/iter_fold.hpp>

Parameters

Parameter	Requirement	Description
`Sequence`	Forward Sequence	A sequence to iterate.
`State`	Any type	The initial state for the first `ForwardOp` application.
`ForwardOp`	Binary Lambda Expression	The operation to be executed on forward traversal.

Expression semantics

For any Forward Sequence s, binary Lambda Expression op, and an arbitrary type state:

typedef iter_fold<s,state,op>::type t;

Return type:

Return type:	A type.
Semantics:	Equivalent to typedef begin<s>::type i₁; typedef apply<op,state,i₁>::type state₁; typedef next<i₁>::type i₂; typedef apply<op,state₁,i₂>::type state₂; ... typedef apply<op,state_n-1,i_n>::type state_n; typedef next<i_n>::type last; typedef state_n t; where `n == size<s>::value` and `last` is identical to `end<s>::type`; equivalent to `typedef state t;` if `empty<s>::value == true`.

A type.

Semantics:

Equivalent to

typedef begin<s>::type i₁;
typedef apply<op,state,i₁>::type state₁;
typedef next<i₁>::type i₂;
typedef apply<op,state₁,i₂>::type state₂;
...
typedef apply<op,state_n-1,i_n>::type state_n;
typedef next<i_n>::type last;
typedef state_n t;

where n == size<s>::value and last is identical to end<s>::type; equivalent to typedef state t; if empty<s>::value == true.

Complexity

Linear. Exactly size<s>::value applications of op.

Example

typedef vector_c<int,5,-1,0,7,2,0,-5,4> numbers;
typedef iter_fold<
      numbers
    , begin<numbers>::type
    , if_< less< deref<_1>, deref<_2> >,_2,_1 >
    >::type max_element_iter;

BOOST_MPL_ASSERT_RELATION( deref<max_element_iter>::type::value, ==, 7 );