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// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.
#if !defined(CPPLINQ_LINQ_TAKE_HPP)
#define CPPLINQ_LINQ_TAKE_HPP
#pragma once
#include <cstddef>
namespace cpplinq
{
template <class InnerCursor>
struct linq_take_cursor
{
typedef typename InnerCursor::element_type element_type;
typedef typename InnerCursor::reference_type reference_type;
typedef typename InnerCursor::cursor_category cursor_category;
linq_take_cursor(const InnerCursor& cur, std::size_t rem) : cur(cur), rem(rem) {}
void forget() { cur.forget(); }
bool empty() const { return cur.empty() || rem == 0; }
void inc() { cur.inc(); --rem; }
reference_type get() const { return cur.get(); }
bool atbegin() const { return cur.atbegin(); }
void dec() { cur.dec(); --rem; }
void skip(std::size_t n) { cur.skip(n); rem -= n; }
std::size_t position() const { return cur.position(); }
std::size_t size() const { return cur.size(); }
private:
InnerCursor cur;
std::size_t rem;
};
namespace detail {
template <class Collection>
linq_take_cursor<typename Collection::cursor>
take_get_cursor_(
const Collection& c,
std::size_t n,
onepass_cursor_tag
)
{
return linq_take_cursor<typename Collection::cursor>(c.get_cursor(), n);
}
template <class Collection>
typename Collection::cursor
take_get_cursor_(
const Collection& c,
std::size_t n,
random_access_cursor_tag
)
{
auto cur = c.get_cursor();
if (cur.size() > n) {
cur.truncate(n);
}
return cur;
}
}
template <class Collection>
struct linq_take
{
typedef typename std::conditional<
util::less_or_equal_cursor_category<
random_access_cursor_tag,
typename Collection::cursor::cursor_category>::value,
typename Collection::cursor,
linq_take_cursor<typename Collection::cursor>>::type
cursor;
linq_take(const Collection& c, std::size_t n) : c(c), n(n) {}
cursor get_cursor() const {
return detail::take_get_cursor_(c, n, typename Collection::cursor::cursor_category());
}
Collection c;
std::size_t n;
};
template <class Collection>
auto get_cursor(
const linq_take<Collection>& take
)
-> decltype(get_cursor_(take, typename Collection::cursor::cursor_category()))
{
return get_cursor_(take, typename Collection::cursor::cursor_category());
}
}
#endif // !defined(CPPLINQ_LINQ_TAKE_HPP)
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