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< html >< head >< title > boost::mpl::fold</ title >
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< h1 >< a href = "../Table_of_Contents.html" >< img src = "../mpl_logo.jpg" alt = "[Home]" border = 0 align = "right" ></ a > fold</ h1 >< h3 > Synopsis</ h3 >
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< p >
< pre >
template<
typename Sequence
, typename State
, typename ForwardOp
>
struct fold
{
typedef < em > unspecified</ em > type;
};
</ pre >
< p >
< h3 > Description</ h3 >
< p >
Returns the result of the successive application of binary < code > ForwardOp</ code > to the result of the previous < code > ForwardOp</ code > invocation (< code > State</ code > if it's the first call) and every element of the sequence in the range < code > [begin< Sequence> ::type,end< Sequence> ::type)</ code > in the linear order.
< p >
< h3 > Definition</ h3 >
< p >
< pre >
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#include "< a href = "../../../../../boost/mpl/fold.hpp" > boost/mpl/fold.hpp</ a > "
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</ pre >
< p >
< h3 > Parameters</ h3 >
< table border = "1" >
< tr >< th > Parameter </ th >< th > Requirement </ th >< th > Description </ th ></ tr >
< tr >< td >< code > Sequence</ code ></ td >< td > A model of < a href = "../Sequence.html" > Sequence</ a ></ td >< td > A sequence to iterate. </ td ></ tr >
< tr >< td >< code > State</ code ></ td >< td > A type</ td >< td > The initial state for the first < code > ForwardOp</ code > application. </ td ></ tr >
< tr >< td >< code > ForwardOp</ code ></ td >< td > A model of [Lambda Function]</ td >< td > The operation to be executed on forward traversal. </ td ></ tr >
</ table >
< p >
< h3 > Expression semantics</ h3 >
< p >
< table border = "1" >
< tr >< th > Expression </ th >< th > Expression type </ th >< th > Precondition </ th >< th > Semantics </ th >< th > Postcondition </ th ></ tr >
< tr >< td >< code > typedef fold< Sequence,T,Op> ::type t;</ code ></ td >< td > A type</ td >< td ></ td >< td > Equivalent to < code > typedef lambda< Op> ::type op; typedef iter_fold< Sequence,T,apply< op,_1,deref< _2> > > ::type t;</ code > .</ td >< td ></ td ></ tr >
</ table >
< p >
< h3 > Complexity</ h3 >
< p >
Linear. Exactly < code >< a href = "../Reference/size.html" > size</ a > < Sequence> ::type::value</ code > applications of < code > ForwardOp</ code > .
< p >
< h3 > Example</ h3 >
< p >
< pre >
typedef < a href = "../Reference/vector.html" > vector</ a > < long,float,short,double,float,long,long double> types;
typedef typename fold<
types
, integral_c< long, 0>
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, if_< is_float< _2> ,next< _1> ,_1 >
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> ::type number_of_floats;
< p >
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BOOST_STATIC_ASSERT(number_of_floats::value == 4);
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</ pre >
< p >
< h3 > See also</ h3 >
< p >
< a href = "../Algorithms.html" > Algorithms</ a > , < code >< a href = "../Reference/fold_backward.html" > fold_backward</ a ></ code > , < code >< a href = "../Reference/iter_fold.html" > iter_fold</ a ></ code > , < code >< a href = "../Reference/iter_fold_backward.html" > iter_fold_backward</ a ></ code > , < code >< a href = "../Reference/copy.html" > copy</ a ></ code > , < code >< a href = "../Reference/copy_if.html" > copy_if</ a ></ code >
< p >< hr >
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< a href = "../Table_of_Contents.html" > Table of Contents</ a >< br > Last edited December 12, 2002 4:42 pm</ body ></ html >
