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libcruft-util/view.hpp
Danny Robson 7e11707c39 view: remove ambiguous operator- 
this operation is identical to the more appropriately named 'consume'
which should be used in its stead.
2018-03-02 12:21:38 +11:00

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/*
* 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 2015-2018 Danny Robson <danny@nerdcruft.net>
*/
#ifndef CRUFT_UTIL_VIEW_HPP
#define CRUFT_UTIL_VIEW_HPP
#include "types/traits.hpp"
#include "maths.hpp"
#include <cstdlib>
#include <ostream>
#include <string>
#include <cstring>
#include <stdexcept>
#include <iterator>
namespace util {
template <typename BeginT, typename EndT = BeginT>
struct view {
public:
//---------------------------------------------------------------------
using value_type = typename std::iterator_traits<
remove_restrict_t<BeginT>
>::value_type;
using size_type = size_t;
//---------------------------------------------------------------------
constexpr
view (const BeginT &first, const EndT &last) noexcept:
m_begin (first),
m_end (last)
{ ; }
template <
typename ContainerT,
typename = std::enable_if_t<is_container_v<std::decay_t<ContainerT>>,void>
>
view (ContainerT &rhs):
view (rhs.begin (), rhs.end ())
{ ; }
template <
typename ContainerT,
typename = std::enable_if_t<is_container_v<std::decay_t<ContainerT>>,void>
>
view (const ContainerT &rhs):
view (rhs.begin (), rhs.end ())
{ ; }
//---------------------------------------------------------------------
// cosntruction from pointer/size represenations for ease of use with
// legacy C code.
template <
typename CountT,
typename = std::enable_if_t<std::is_integral_v<CountT>,void>
>
view (
const BeginT &_begin,
CountT _size
):
view (_begin, _begin + _size)
{ ; }
//---------------------------------------------------------------------
// implicit conversion from const pointer const views to const pointer views
template <
typename ValueT,
typename = std::enable_if_t<
std::is_same_v<BeginT, const ValueT**> &&
std::is_same_v<EndT, const ValueT**>
>
>
view (const view<const ValueT*const*,const ValueT*const*> &rhs):
m_begin (const_cast<const ValueT**> (rhs.begin ())),
m_end (const_cast<const ValueT**> (rhs.end ()))
{ ; }
//---------------------------------------------------------------------
// implicit conversion from pointer views to const pointer views
template <
typename ValueT,
typename = std::enable_if_t<
std::is_same_v<BeginT, const ValueT*> &&
std::is_same_v<EndT, const ValueT*>
>
>
view (const view<ValueT*,ValueT*> &rhs):
m_begin (rhs.begin ()),
m_end (rhs.end ())
{ ; }
//---------------------------------------------------------------------
// explicitly cater for the char array case so that we don't
// accidentally include the trailing null in the data.
template <std::size_t N>
view (const char (&value)[N]):
view {std::begin (value), std::begin (value) + N - 1}
{
static_assert (N > 0);
}
//---------------------------------------------------------------------
view (const char *str):
view { str, str + strlen (str) }
{ ; }
//---------------------------------------------------------------------
view (char *str):
view (str, str + strlen (str))
{ ; }
//---------------------------------------------------------------------
template <std::size_t N>
view (char (&value)[N]):
view {std::begin (value), std::begin (value) + N - 1}
{
static_assert (N > 0);
}
//---------------------------------------------------------------------
template <std::size_t N, typename ValueT>
view (const ValueT(&value)[N]):
view {std::begin (value), std::end (value)}
{ ; }
//---------------------------------------------------------------------
template <std::size_t N, typename ValueT>
view (ValueT(&value)[N]):
view {std::begin (value), std::end (value)}
{ ; }
//---------------------------------------------------------------------
constexpr
view (const view &rhs) noexcept:
view {rhs.m_begin, rhs.m_end}
{ ; }
//---------------------------------------------------------------------
// technically we could get away without explicitly defining a move
// constructor here, but by nulling rhs we can more easily use this
// class as a base for unique owning pointers without exposing the
// begin/end data members to them directly.
constexpr view (view &&rhs) noexcept:
view {std::move (rhs.m_begin), std::move (rhs.m_end)}
{ ; }
//---------------------------------------------------------------------
// allow null construction of views where IteratorT is constructible
// from nullptr_t
//
// ideally we would avoid exposing this as it promotes use of nulls but
// it simplifies construction of views that are data members of classes
// when we may not immediately know the values we should contain.
constexpr view (std::nullptr_t) noexcept:
view {nullptr,nullptr}
{ ; }
//---------------------------------------------------------------------
template <typename CharT, typename Traits, typename Allocator>
view (std::basic_string<CharT,Traits,Allocator> &val):
view (std::data (val), std::data (val) + std::size (val))
{ ; }
//---------------------------------------------------------------------
template <typename CharT, typename Traits, typename Allocator>
view (const std::basic_string<CharT,Traits,Allocator> &val):
view (std::data (val), std::data (val) + std::size (val))
{ ; }
//---------------------------------------------------------------------
template <typename ValueT, typename AllocatorT>
view (const std::vector<ValueT,AllocatorT> &rhs):
view (std::data (rhs), std::data (rhs) + std::size (rhs))
{ ; }
//---------------------------------------------------------------------
template <typename ValueT, typename AllocatorT>
view (std::vector<ValueT,AllocatorT> &rhs):
view (std::data (rhs), std::data (rhs) + std::size (rhs))
{ ; }
//---------------------------------------------------------------------
template <typename ValueT, std::size_t N>
view (std::array<ValueT,N> &rhs):
view (std::data (rhs), std::data (rhs) + std::size (rhs))
{ ; }
//---------------------------------------------------------------------
template <typename ValueT, std::size_t N>
view (const std::array<ValueT,N> &rhs):
view (std::data (rhs), std::data (rhs) + std::size (rhs))
{ ; }
//---------------------------------------------------------------------
view&
operator= (const view &rhs) noexcept
{
m_begin = rhs.m_begin;
m_end = rhs.m_end;
return *this;
}
//---------------------------------------------------------------------
view&
operator= (view &&rhs) noexcept
{
m_begin = rhs.m_begin;
m_end = rhs.m_end;
rhs.m_begin = BeginT{};
rhs.m_end = EndT{};
return *this;
};
///////////////////////////////////////////////////////////////////////
constexpr BeginT begin (void) noexcept { return m_begin; }
constexpr EndT end (void) noexcept { return m_end; }
//---------------------------------------------------------------------
constexpr const BeginT begin (void) const noexcept { return cbegin (); }
constexpr const EndT end (void) const noexcept { return cend (); }
//---------------------------------------------------------------------
constexpr const BeginT cbegin (void) const noexcept { return m_begin; }
constexpr const EndT cend (void) const noexcept { return m_end; }
//---------------------------------------------------------------------
auto data (void) noexcept { return begin (); }
auto data (void) const noexcept { return begin (); }
///////////////////////////////////////////////////////////////////////
constexpr bool
empty (void) const noexcept
{
return m_begin == m_end;
}
//---------------------------------------------------------------------
// the return type of size _should_ be whatever std::distance returns,
// or something else that makes sense for the iterators we've been
// handed.
//
// but it's a pain in the arse to use sizes that aren't unsigned given
// that other libraries need to compare sizes pretty often and
// everything else in the world tends to be unsigned.
constexpr auto
size (void) const noexcept
{
return static_cast<size_type> (std::distance (m_begin, m_end));
}
//---------------------------------------------------------------------
[[nodiscard]] constexpr auto
redim (size_type count) const
{
assert (count > 0);
if (count > size ())
throw std::invalid_argument ("redim to higher size not allowed");
return view { m_begin, m_begin + count };
};
//---------------------------------------------------------------------
constexpr std::tuple<
util::view<BeginT,BeginT>,
util::view<BeginT,EndT>
>
split (BeginT pos) const
{
return {
{ m_begin, pos },
{ pos, m_end }
};
}
//---------------------------------------------------------------------
constexpr auto
split (int pos) const
{
auto last = m_begin;
std::advance (last, pos);
return split (last);
}
//---------------------------------------------------------------------
// slices a view using python indexing semantics. ie,
// "abc".slice(0, 3) == "abc"
// "abc".slice(0, -1) == "abc"
// "abc".slice(0, -2) == "ab"
constexpr auto
slice (int a, int b)
{
auto first = m_begin;
auto last = m_begin;
std::advance (first, a < 0 ? size () + a + 1 : a);
std::advance (last, b < 0 ? size () + b + 1 : b);
return util::view { first, last };
}
//---------------------------------------------------------------------
constexpr auto
consume (int count) const
{
auto [a,b] = split (count);
(void)a;
return b;
}
//---------------------------------------------------------------------
constexpr util::view<BeginT,EndT>
consume (util::view<BeginT,BeginT> prefix) const
{
assert (prefix.begin () == begin ());
return { prefix.end (), end () };
}
constexpr util::view<BeginT,EndT>
consume (const BeginT pos) const
{
return { pos, end () };
}
///////////////////////////////////////////////////////////////////////
template <
typename ValueT,
typename = std::enable_if_t<
std::is_pointer_v<BeginT> &&
sizeof (*std::declval<BeginT> ()) == sizeof (ValueT)
,
void
>
>
view<ValueT*>
cast (void) const
{
return {
reinterpret_cast<ValueT*> (m_begin),
reinterpret_cast<ValueT*> (m_end)
};
}
///////////////////////////////////////////////////////////////////////
constexpr auto&
operator[] (size_t idx)& noexcept
{
auto it = begin ();
std::advance (it, idx);
return *it;
}
//---------------------------------------------------------------------
constexpr auto&
operator[] (size_t idx) const& noexcept
{
auto it = begin ();
std::advance (it, idx);
return *it;
}
private:
///////////////////////////////////////////////////////////////////////
BeginT m_begin;
EndT m_end;
};
//-------------------------------------------------------------------------
template <typename ValueT, std::size_t N>
view (const ValueT(&)[N]) -> view<const ValueT*,const ValueT*>;
//-------------------------------------------------------------------------
view (const char*) -> view<const char*, const char*>;
view (char*) -> view<char*>;
//-------------------------------------------------------------------------
template <
typename IteratorT,
typename SizeT,
typename = std::enable_if_t<
std::is_integral_v<SizeT>,void
>
>
view (IteratorT, SizeT) -> view<IteratorT,IteratorT>;
template <typename CharT, typename Traits, typename Allocator>
view (std::basic_string<CharT,Traits,Allocator> &) -> view<typename Allocator::pointer>;
template <typename CharT, typename Traits, typename Allocator>
view (const std::basic_string<CharT,Traits,Allocator> &) -> view<typename Allocator::const_pointer>;
template <typename ValueT, typename AllocatorT>
view (std::vector<ValueT,AllocatorT>&) -> view<typename AllocatorT::pointer>;
template <typename ValueT, typename AllocatorT>
view (const std::vector<ValueT,AllocatorT>&) -> view<typename AllocatorT::const_pointer>;
template <typename ValueT, std::size_t N>
view (std::array<ValueT,N>) -> view<ValueT*>;
template <typename ContainerT>
view (ContainerT&) -> view<
typename ContainerT::iterator
>;
template <typename ContainerT>
view (const ContainerT&) -> view<
typename ContainerT::const_iterator
>;
///////////////////////////////////////////////////////////////////////////
template <typename ValueT, size_t N>
auto
make_view (const ValueT (&arr)[N])
{
return util::view<const ValueT*> (arr + 0, arr + N);
}
//-------------------------------------------------------------------------
template <typename ContainerT>
auto
make_view (ContainerT &t)
{
return util::view<decltype(std::begin (t))> { std::begin (t), std::end (t) };
}
//-------------------------------------------------------------------------
template <typename ContainerT>
auto
make_view (const ContainerT &t)
{
return util::view<decltype(std::cbegin (t))> { std::cbegin (t), std::cend (t) };
}
//-------------------------------------------------------------------------
// disable the possibility of creating a view to a temporary. note that
// this only works if an lval version has already been defined otherwise
// universal reference rules will capture both lval and rval here.
template <typename ContainerT>
auto
make_view (ContainerT&&) = delete;
///////////////////////////////////////////////////////////////////////////
template <typename ContainerT>
auto
make_cview (const ContainerT &t)
{
return make_view (t);
//return util::view<decltype(std::cbegin (t))> { std::cbegin (t), std::cend (t) };
}
//-------------------------------------------------------------------------
template <typename BeginT, typename EndT>
auto
make_view (BeginT first, EndT last)
{
return view<BeginT, EndT> {first, last};
}
//-------------------------------------------------------------------------
template <typename ValueT>
auto
make_cview (ValueT *first, ValueT *last)
{
return view<const ValueT*> {first, last};
}
///////////////////////////////////////////////////////////////////////////
inline
view<const char*> make_view (const char *str)
{
return { str, str + strlen (str) };
}
//-------------------------------------------------------------------------
inline
view<char*> make_view (char *str)
{
return { str, str + strlen (str) };
}
//-------------------------------------------------------------------------
template <typename CharT, typename TraitsT, typename AllocT>
view<const CharT*>
make_view (const std::basic_string<CharT,TraitsT,AllocT> &str)
{
return {
std::data (str),
std::data (str) + std::size (str)
};
}
//-------------------------------------------------------------------------
template <typename CharT, typename TraitsT, typename AllocT>
view<CharT*>
make_view (std::basic_string<CharT,TraitsT,AllocT> &str)
{
return {
std::data (str),
std::data (str) + std::size (str)
};
}
//-------------------------------------------------------------------------
template <typename CharT, typename TraitsT, typename AllocT>
view<const CharT*>
make_view (const std::basic_string<CharT,TraitsT,AllocT>&&) = delete;
//-------------------------------------------------------------------------
template <typename CharT, typename TraitsT, typename AllocT>
view<CharT*>
make_view (std::basic_string<CharT,TraitsT,AllocT>&&) = delete;
///////////////////////////////////////////////////////////////////////////
// calculates a byte oriented view over an arbitrary type
//
// useful for passing in memory structures to file descriptors and the
// like. but the consequences of endian conversion is on the user...
template <typename T>
view<std::byte*>
make_byte_view (T &t)
{
auto first = reinterpret_cast<std::byte*> (&t);
auto last = first + sizeof (t);
return { first, last };
}
//-------------------------------------------------------------------------
template <typename T>
view<std::byte*>
make_byte_view (T&&) = delete;
//-------------------------------------------------------------------------
template <typename T>
view<const std::byte*>
make_byte_view (const T &t)
{
auto first = reinterpret_cast<std::byte*> (&t);
auto last = first + sizeof (t);
return { first, last };
}
//-------------------------------------------------------------------------
template <typename T>
view<const std::byte*>
make_byte_view (const T &&t) = delete;
///////////////////////////////////////////////////////////////////////////
template <
typename BeginA, typename EndA,
typename BeginB, typename EndB
>
constexpr bool
equal (const view<BeginA,EndA> &a, const view<BeginB,EndB> &b)
{
return a.size () == b.size () &&
std::equal (std::begin (a), std::end (a), std::begin (b));
}
//-------------------------------------------------------------------------
// defer equality to the view/view operator by way of make_view
template <
typename IteratorA,
typename IteratorB,
typename ValueT,
typename = std::enable_if_t<
!std::is_same_v<ValueT, view<IteratorA,IteratorB>>,
void
>
>
constexpr bool
equal (const view<IteratorA,IteratorB> &a, const ValueT &b)
{
return equal (a, make_view (b));
}
//-------------------------------------------------------------------------
// reverse the arguments and forward to the above operator. we formumlate
// equality this way to avoid implementing the operator twice for each
// weird case.
template <
typename IteratorA,
typename IteratorB,
typename ValueT,
typename = std::enable_if_t<
!std::is_same_v<ValueT, view<IteratorA,IteratorB>>,
void
>
>
constexpr bool
equal (const ValueT &a, const view<IteratorA,IteratorB> &b)
{
return equal (b, a);
}
///////////////////////////////////////////////////////////////////////////
template <typename IteratorA, typename IteratorB>
constexpr bool
operator== (const view<IteratorA,IteratorB> &a, const view<IteratorA,IteratorB> &b)
{
return a.begin () == b.begin () && a.end () == b.end ();
}
//-------------------------------------------------------------------------
template <typename IteratorA, typename IteratorB>
constexpr bool
operator!= (const view<IteratorA,IteratorB> &a, const view<IteratorA,IteratorB> &b)
{
return !(a == b);
}
//-------------------------------------------------------------------------
template <
typename IteratorA,
typename IteratorB,
typename ValueT,
typename = std::enable_if_t<
!std::is_same_v<ValueT, view<IteratorA,IteratorB>>,
void
>
>
constexpr bool
operator!= (const view<IteratorA,IteratorB> &a, const ValueT &b)
{
return !(a == b);
}
//-------------------------------------------------------------------------
template <
typename IteratorA,
typename IteratorB,
typename ValueT,
typename = std::enable_if_t<
!std::is_same_v<ValueT, view<IteratorA,IteratorB>>,
void
>
>
constexpr bool
operator!= (const ValueT &a, const view<IteratorA,IteratorB> &b)
{
return !(a == b);
}
///////////////////////////////////////////////////////////////////////////
template <typename BeginT, typename EndT>
std::ostream&
operator<< (std::ostream &os, view<BeginT, EndT> val)
{
std::copy (
std::cbegin (val),
std::cend (val),
std::ostream_iterator<typename decltype(val)::value_type> (os)
);
return os;
}
///////////////////////////////////////////////////////////////////////////
/// a basic stringlike comparison operator that behaves as
/// std::string::compare would.
///
/// provided so that the common case of stringlike views can be used in a
/// std::map and similar without a great deal of work.
inline bool
operator< (util::view<const char*> a, util::view<const char*> b)
{
const auto la = std::size (a);
const auto lb = std::size (b);
const auto res = strncmp (
std::data (a),
std::data (b),
util::min (la, lb)
);
return res < 0 || (res == 0 && la < lb);
}
}
#endif
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