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iterator: improve reference semantics

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This commit is contained in:
Danny Robson 2018-03-27 15:49:47 +11:00
parent 93185775e6
commit 1b023f7c8d
3 changed files with 127 additions and 103 deletions
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137
iterator.hpp
View File

@ -22,6 +22,7 @@
#include "variadic.hpp"
#include "view.hpp"
#include <iterator>
template <typename Base>
class referencing_iterator {
@ -283,53 +284,22 @@ namespace util {
///////////////////////////////////////////////////////////////////////////
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.
//
// IteratorT: a tuple of iterators across all containers
//
// StoreT: a tuple of containers we own. used when we were provided
// with an rval at zip time. allows us to destroy the data
// when we're actually done iterating.
template <
typename IteratorT,
typename StoreT,
typename I = std::make_index_sequence<std::tuple_size<IteratorT>::value>
typename = std::make_index_sequence<std::tuple_size_v<IteratorT>>
>
class collection;
struct iterator;
//---------------------------------------------------------------------
template <
typename IteratorT,
typename StoreT,
std::size_t ...I
>
class collection<
IteratorT,
StoreT,
std::index_sequence<I...>
> {
template <typename IteratorT, std::size_t ...Indices>
struct iterator<IteratorT, std::index_sequence<Indices...>> {
public:
collection (IteratorT _begin, IteratorT _end, StoreT &&_store):
m_begin { _begin },
m_end { _end },
m_store { std::forward<StoreT> (_store) }
{ ; }
// we cannot be a forward iterator because we don't want to supply
// references to a value type as that would necessitate storing
// said value types within the iterator.
using iterator_category = std::input_iterator_tag;
using difference_type = std::ptrdiff_t;
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 (IteratorT _iterators):
m_iterators (_iterators)
{ ; }
@ -338,21 +308,17 @@ namespace util {
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)...);
std::tuple (++std::get<Indices> (m_iterators)...);
return *this;
}
iterator operator++ (int);
auto
operator* (void)
{
return std::make_tuple (*std::get<I> (m_iterators)...);
return std::forward_as_tuple (*std::get<Indices> (m_iterators)...);
}
@ -374,24 +340,60 @@ namespace util {
};
iterator
begin (void)
{
return iterator { { std::get<I> (m_begin)... } };
}
// 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.
//
// we have to store begin and end iterators because we might not have
// enough information to determine the correct types from StoreT;
// eg, in the case of arrays that have decayed to pointers we can't
// find the end.
//
// BeginT: a tuple of begin iterators across all containers
//
// EndT: a tuple of end iterators across all containers
//
// StoreT: a tuple of containers we might own. used when we were
// provided with an rval at zip time. allows us to destroy the
// data when we're actually done iterating.
template <
typename StoreT,
typename BeginT,
typename EndT,
typename I = std::make_index_sequence<std::tuple_size_v<StoreT>>
>
class collection;
iterator
end (void)
{
return iterator { { std::get<I> (m_end)... } };
}
//---------------------------------------------------------------------
template <
typename StoreT,
typename BeginT,
typename EndT,
std::size_t ...I
>
class collection<
StoreT,
BeginT,
EndT,
std::index_sequence<I...>
> {
public:
collection (StoreT _store, BeginT _begin, EndT _end):
m_store { std::move (_store) },
m_begin (std::move (_begin)),
m_end (std::move (_end))
{ ; }
auto begin (void)& { return iterator<BeginT> { m_begin }; }
auto end (void)& { return iterator<EndT> { m_end }; }
private:
IteratorT m_begin;
IteratorT m_end;
const StoreT m_store;
StoreT m_store;
BeginT m_begin;
EndT m_end;
};
}
@ -408,19 +410,16 @@ namespace util {
auto
zip (ContainerT&&... data)
{
using IteratorT = std::tuple<decltype(std::begin(data))...>;
auto store = util::variadic::filter<std::is_rvalue_reference> (std::forward<ContainerT> (data)...);
return detail::zip::collection<
IteratorT,
decltype(store),
decltype (std::forward_as_tuple (data...)),
decltype (std::make_tuple (std::begin (data)...)),
decltype (std::make_tuple (std::end (data)...)),
std::make_index_sequence<sizeof...(ContainerT)>
> {
> (
std::forward_as_tuple (data...),
std::make_tuple (std::begin (data)...),
std::make_tuple (std::end (data)...),
std::move (store)
};
std::make_tuple (std::end (data)...)
);
};

28
test/iterator.cpp
View File

@ -12,12 +12,17 @@ main (int, char**)
{
util::TAP::logger tap;
// test that iteration across disparate types works as expected.
//
// the char array is an important element because it tends to decay to a
// pointer type unless we're paying careful attention.
{
std::vector<int> v_int { 1, 2, 3 };
std::array<float,3> a_float { 1.1f, 2.2f, 3.3f };
char c_char[] = { 'a', 'b', 'c' };
char c_char[] = { '\0', 'b', 'c' };
bool success = true;
for (const auto &[i, v, a, c]: util::izip (v_int, a_float, c_char)) {
for (auto [i, v, a, c]: util::izip (v_int, a_float, c_char)) {
success = success &&
v_int[i] == v &&
util::equal (a_float[i], a) &&
@ -25,5 +30,24 @@ main (int, char**)
}
tap.expect (success, "izip containers of int, float, and char and an initialiser_list");
}
// test that the obvious structured binding syntax gives references to
// the underlying values rather than silently supplying lvalues.
//
// we deliberately do not use any type of references in the range loop so
// that we check the syntax a user is likely to employ actually works.
// references may not be an obvious consideration.
{
const std::array<unsigned,3> src { 0, 1, 2 };
std::array<unsigned,3> dst { 2, 0, 1 };
for (auto [a,b]: util::zip (src, dst))
b = a;
tap.expect_eq (src, dst, "copy using structured bindings");
}
return tap.status ();
}

3
test/string.cpp
View File

@ -30,8 +30,9 @@ main (int, char**)
};
util::view src { csv.c_str (), csv.size () };
for (const auto &[tok, expected]: util::zip (util::tokeniser (src, ','), TESTS))
for (auto &&[tok, expected]: util::zip (util::tokeniser (src, ','), TESTS)) {
tap.expect (equal (tok, expected.value), "%s", expected.message);
}
return tap.status ();
}