libcruft-util/iterator.hpp

379 lines
12 KiB
C++

/*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* Copyright 2010-2012 Danny Robson <danny@nerdcruft.net>
*/
#ifndef __UTIL_ITERATOR_HPP
#define __UTIL_ITERATOR_HPP
#include "types/traits.hpp"
#include "variadic.hpp"
template <typename Base>
class referencing_iterator {
protected:
typedef typename std::enable_if<
is_dereferencable<
typename Base::value_type
>::value,
typename Base::value_type
>::type base_value_type;
public:
typedef typename dereferenced_type<base_value_type>::type value_type ;
typedef typename Base::difference_type difference_type ;
typedef value_type& reference ;
typedef value_type* pointer;
typedef typename Base::iterator_category iterator_category;
protected:
Base m_base;
public:
explicit referencing_iterator (Base _base):
m_base (_base)
{ ; }
referencing_iterator& operator++() { ++m_base; return *this; }
referencing_iterator operator++(int) { auto val = *this; ++m_base; return val; }
bool operator== (const referencing_iterator<Base> &rhs) { return m_base == rhs.m_base; }
bool operator!= (const referencing_iterator<Base> &rhs) { return m_base != rhs.m_base; }
bool operator>= (const referencing_iterator<Base> &rhs) { return m_base >= rhs.m_base; }
bool operator<= (const referencing_iterator<Base> &rhs) { return m_base <= rhs.m_base; }
bool operator> (const referencing_iterator<Base> &rhs) { return m_base > rhs.m_base; }
bool operator< (const referencing_iterator<Base> &rhs) { return m_base < rhs.m_base; }
const value_type& operator*() const
{ return **m_base; }
reference operator*()
{ return **m_base; }
difference_type operator-(const referencing_iterator<Base>& rhs) const { return m_base - rhs.m_base; }
referencing_iterator<Base> operator-(int rhs) const { return referencing_iterator (m_base - rhs); }
referencing_iterator<Base> operator+(int rhs) const { return referencing_iterator (m_base + rhs); }
};
namespace util {
///////////////////////////////////////////////////////////////////////////
/// an output iterator that inserts a delimiter between successive
/// assignments
///
/// very useful for outputting comma seperated lists to an ostream, eg:
///
/// std::copy (
/// std::cbegin (container),
/// std::cend (container),
/// util::infix_iterator<value_type> (os, ", ")
/// );
template <
typename T,
class CharT = char,
class Traits = std::char_traits<CharT>
>
class infix_iterator : public std::iterator<std::output_iterator_tag, void, void, void, void> {
public:
using char_type = CharT;
using traits_type = Traits;
using ostream_type = std::basic_ostream<char_type, traits_type>;
infix_iterator (ostream_type& _output, const CharT *_delimiter):
m_output (_output),
m_delimiter (_delimiter)
{ ; }
infix_iterator&
operator= (const T &value)
{
if (!m_first)
m_output << m_delimiter;
m_output << value;
m_first = false;
return *this;
}
infix_iterator& operator* (void) { return *this; }
infix_iterator& operator++ (void) { return *this; }
infix_iterator& operator++ (int) { return *this; }
private:
bool m_first = true;
ostream_type &m_output;
const CharT *m_delimiter;
};
namespace detail {
template <typename ContainerT, typename CharT>
struct infix_t {
const ContainerT &_container;
const CharT *_delimiter;
};
template <typename ContainerT, typename CharT>
std::ostream&
operator<< (std::ostream &os, const infix_t<ContainerT,CharT> &val)
{
std::copy (std::cbegin (val._container),
std::cend (val._container),
infix_iterator<typename ContainerT::value_type> (os, val._delimiter));
return os;
}
};
/// a helper function that returns an object that will use a
/// util::infix_iterator to output a container's values to an ostream with
/// the given delimiter.
///
/// reduces boilerplate code required to output lists of things
template <typename ContainerT, typename CharT = char>
auto
make_infix (const ContainerT &_container, const CharT *_delimiter = ", ")
{
return detail::infix_t<ContainerT,CharT> { _container, _delimiter };
};
///////////////////////////////////////////////////////////////////////////
template <typename ContainerT>
class indices {
public:
indices (const ContainerT &_container):
m_container (_container)
{ ; }
class iterator : public std::iterator<std::forward_iterator_tag, std::size_t, std::size_t> {
public:
iterator (std::size_t _index):
m_index (_index)
{ ; }
bool
operator!= (const iterator &rhs) const
{
return m_index != rhs.m_index;
}
bool
operator== (const iterator &rhs) const
{
return m_index == rhs.m_index;
}
iterator&
operator++ (void) &
{
++m_index;
return *this;
};
const std::size_t&
operator* (void) const&
{
return m_index;
}
private:
std::size_t m_index;
};
iterator begin (void) const { return iterator { 0 }; }
iterator end (void) const { return iterator { m_container.size () }; }
private:
const ContainerT &m_container;
};
//-------------------------------------------------------------------------
template <typename T>
indices<T>
make_indices (const T &_t)
{
return indices<T> (_t);
}
///////////////////////////////////////////////////////////////////////////
namespace detail::zip {
// holds a tuple of iterators for begin and end, and returns an
// iterator that transforms these iterators into tuples of value_types.
//
// this must be expressed in terms of iterators, rather than containers,
// because it dramatically simplifies iterating over raw arrays.
template <
typename IteratorT,
typename I = std::make_index_sequence<std::tuple_size<IteratorT>::value>
>
class collection;
//---------------------------------------------------------------------
template <
typename IteratorT,
std::size_t ...I
>
class collection<
IteratorT,
std::index_sequence<I...>
> {
public:
collection (const IteratorT &_begin, const IteratorT &_end):
m_begin { _begin },
m_end { _end }
{ ; }
struct iterator : std::iterator<
std::forward_iterator_tag,
std::tuple<
typename std::iterator_traits<
typename std::tuple_element<I,IteratorT>::type
>::value_type...
>,
std::size_t
> {
public:
iterator (const IteratorT &_iterators):
m_iterators (_iterators)
{ ; }
iterator&
operator++ (void)
{
// HACK: we don't actually need to create a tuple here,
// but it's a zero cost method to expand the parameter
// pack.
std::make_tuple (++std::get<I> (m_iterators)...);
return *this;
}
iterator operator++ (int);
auto
operator* (void)
{
return std::make_tuple (*std::get<I> (m_iterators)...);
}
bool
operator== (const iterator &rhs) const
{
return m_iterators == rhs.m_iterators;
}
bool
operator!= (const iterator &rhs) const
{
return !(*this == rhs);
}
private:
IteratorT m_iterators;
};
iterator
begin (void)
{
return iterator { { std::get<I> (m_begin)... } };
}
iterator
end (void)
{
return iterator { { std::get<I> (m_end)... } };
}
private:
IteratorT m_begin;
IteratorT m_end;
};
}
///------------------------------------------------------------------------
/// takes a variable number of container arguments and returns an interable
/// object with a value_type of tuple of the argument's value_types.
///
/// the returned iterator value_type is suitable for using in range-for
/// and structured bindings (and really, that's the entire point here).
///
/// eg, util::zip ({1,2,3}, {4,5,6}) ~= {{1,4},{2,5},{3,6}}
template <typename ...ContainerT>
auto
zip (const ContainerT&... data)
{
using IteratorT = std::tuple<decltype(std::begin(data))...>;
return detail::zip::collection<
IteratorT,
std::make_index_sequence<sizeof...(ContainerT)>
> {
std::make_tuple (std::begin (data)...),
std::make_tuple (std::end (data)...)
};
};
///------------------------------------------------------------------------
/// takes a variable number of containers and returns a zipped iterable
/// object where the first of the iterator's value_types is the index of
/// that iterator. ie, it combines container offsets with value_types.
///
/// eg, util::izip ("abc") ~= {{0,'a'},{1,'b'},{2,'c'}}
template <typename ...ContainerT>
auto
izip (const ContainerT&... data)
{
return zip (
::util::make_indices (::util::variadic::first (data...)),
data...
);
}
///////////////////////////////////////////////////////////////////////////
/// an output iterator that always discards any parameters on assignment.
///
/// sometimes useful to pass to algorithms that generate useful results as
/// a return value, while not caring about the implicit OutputIterator
/// results.
struct discard_iterator : public std::iterator<std::output_iterator_tag, discard_iterator> {
template <typename T>
void operator= (const T&) { ; }
discard_iterator& operator++ ( ) { return *this; }
discard_iterator operator++ (int) { return *this; }
discard_iterator& operator* ( ) { return *this; }
};
};
#endif