reverse_fold

Description

For a sequence seq, initial state initial_state, and binary function object or function pointer f, reverse_fold returns the result of the repeated application of binary f to the result of the previous f invocation (inital_state if it is the first call) and each element of seq.

Synopsis

template<
    typename Sequence,
    typename State,
    typename F
    >
typename result_of::reverse_fold<Sequence, State const, F>::type reverse_fold(
    Sequence& seq, State const& initial_state, F f);

template<
    typename Sequence,
    typename State,
    typename F
    >
typename result_of::reverse_fold<Sequence const, State const, F>::type reverse_fold(
    Sequence const& seq, State const& initial_state, F f);

template<
    typename Sequence,
    typename State,
    typename F
    >
typename result_of::reverse_fold<Sequence, State, F>::type reverse_fold(
    Sequence& seq, State& initial_state, F f);

template<
    typename Sequence,
    typename State,
    typename F
    >
typename result_of::reverse_fold<Sequence const, State, F>::type reverse_fold(
    Sequence const& seq, State& initial_state, F f);

Table 1.41. Parameters

Parameter	Requirement	Description
`seq`	A model of Bidirectional Sequence	Operation's argument
`initial_state`	Any type	Initial state
`f`	`f(s,e)` with return type `boost::result_of<F(S,E)>::type` for current state `s` of type `S`, and for each element `e` of type `E` in `seq`	Operation's argument

Expression Semantics

reverse_fold(seq, initial_state, f);

Return type: Any type

Semantics: Equivalent to f(... f(f(initial_state,eN),eN-1) ...e1) where e1 ...eN are the consecutive elements of seq.

Complexity

Linear, exactly result_of::size<Sequence>::value applications of f.

Header

#include <boost/fusion/algorithm/iteration/reverse_fold.hpp>
#include <boost/fusion/include/reverse_fold.hpp>

Example

struct make_string
{
    typedef std::string result_type;

    template<typename T>
    std::string operator()(const std::string& str, const T& t) const
    {
        return str + boost::lexical_cast<std::string>(t);
    }
};
...
const vector<int,int> vec(1,2);
assert(reverse_fold(vec,std::string(""), make_string()) == "21");