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// Copyright (C) 2008-2018 Lorenzo Caminiti
// Distributed under the Boost Software License, Version 1.0 (see accompanying
// file LICENSE_1_0.txt or a copy at http://www.boost.org/LICENSE_1_0.txt).
// See: http://www.boost.org/doc/libs/release/libs/contract/doc/html/index.html
#include <boost/contract/call_if.hpp>
#include <type_traits>
#include <iterator>
#include <functional> // std::bind for generic lambdas.
#include <vector>
#include <list>
#include <sstream>
template<typename Iter>
struct is_random_access_iterator : std::is_same<
typename std::iterator_traits<Iter>::iterator_category,
std::random_access_iterator_tag
> {};
template<typename Iter>
struct is_bidirectional_iterator : std::is_same<
typename std::iterator_traits<Iter>::iterator_category,
std::bidirectional_iterator_tag
> {};
template<typename Iter>
struct is_input_iterator : std::is_same<
typename std::iterator_traits<Iter>::iterator_category,
std::input_iterator_tag
> {};
//[call_if_cxx14
template<typename Iter, typename Dist>
void myadvance(Iter& i, Dist n) {
Iter* p = &i; // So captures change actual pointed iterator value.
boost::contract::call_if<is_random_access_iterator<Iter> >(
std::bind([] (auto p, auto n) { // C++14 generic lambda.
*p += n;
}, p, n)
).template else_if<is_bidirectional_iterator<Iter> >(
std::bind([] (auto p, auto n) {
if(n >= 0) while(n--) ++*p;
else while(n++) --*p;
}, p, n)
).template else_if<is_input_iterator<Iter> >(
std::bind([] (auto p, auto n) {
while(n--) ++*p;
}, p, n)
).else_(
std::bind([] (auto false_) {
static_assert(false_, "requires at least input iterator");
}, std::false_type()) // Use constexpr value.
);
}
//]
struct x {}; // Test not an iterator (static_assert failure in else_ above).
namespace std {
template<>
struct iterator_traits<x> {
typedef void iterator_category;
};
}
int main() {
std::vector<char> v;
v.push_back('a');
v.push_back('b');
v.push_back('c');
v.push_back('d');
std::vector<char>::iterator r = v.begin(); // Random iterator.
myadvance(r, 1);
assert(*r == 'b');
std::list<char> l(v.begin(), v.end());
std::list<char>::iterator b = l.begin(); // Bidirectional iterator.
myadvance(b, 2);
assert(*b == 'c');
std::istringstream s("a b c d");
std::istream_iterator<char> i(s);
myadvance(i, 3);
assert(*i == 'd');
// x j;
// myadvance(j, 0); // Error (correctly because x not even input iter).
return 0;
}
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