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libcruft-util/view.hpp
Danny Robson 644cae506f view: move alignment test for cast into the implementation 
Moving the alignment test from SFINAE into the implementation as a
static_assert means that users don't need to include the implementation
for types where `cast` isn't called. Otherwise, iterator_traits requires
a definition to work with.
2019-05-15 13:03:38 +10:00

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/*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*
* Copyright 2015-2019 Danny Robson <danny@nerdcruft.net>
*/
#pragma once
#include "annotation.hpp"
#include "cast.hpp"
#include "debug.hpp"
#include "maths.hpp"
#include "platform.hpp"
#include "types/traits.hpp"
#include <cstdlib>
#include <iosfwd>
#include <string>
#include <cstring>
#include <stdexcept>
#include <iterator>
#include <type_traits>
namespace cruft {
template <typename BeginT, typename EndT = BeginT>
struct view {
public:
using begin_type = BeginT;
using end_type = EndT;
//---------------------------------------------------------------------
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)
{
if constexpr (cruft::is_lteq_orderable_v<BeginT,EndT>) {
CHECK_LE (m_begin, m_end);
}
}
template <
typename ContainerT,
typename = std::void_t<
decltype (std::declval<ContainerT&> ().begin ()),
decltype (std::declval<ContainerT&> ().end ())
>
>
view (ContainerT &rhs) noexcept (
noexcept (std::declval<ContainerT> ().begin ()) &&
noexcept (std::declval<ContainerT> ().end ())
)
: view (rhs.begin (), rhs.end ())
{ ; }
template <
typename ContainerT,
typename = std::void_t<
decltype (std::declval<ContainerT const&> ().begin ()),
decltype (std::declval<ContainerT const&> ().end ())
>
>
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>
>
constexpr 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):
view (
const_cast<const ValueT**> (rhs.begin ()),
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):
view (rhs.begin (), 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 &) noexcept = default;
constexpr view (view &&) noexcept = default;
view& operator= (const view &rhs) noexcept = default;
view& operator= (view &&rhs) noexcept = default;
//---------------------------------------------------------------------
// 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::size (val))
{ ; }
//---------------------------------------------------------------------
template <typename CharT, typename Traits, typename Allocator>
view (const std::basic_string<CharT,Traits,Allocator> &val):
view (std::data (val), std::size (val))
{ ; }
//---------------------------------------------------------------------
template <typename ValueT, typename AllocatorT>
view (const std::vector<ValueT,AllocatorT> &rhs):
view (std::data (rhs), std::size (rhs))
{ ; }
//---------------------------------------------------------------------
template <typename ValueT, typename AllocatorT>
view (std::vector<ValueT,AllocatorT> &rhs):
view (std::data (rhs), std::size (rhs))
{ ; }
//---------------------------------------------------------------------
template <typename ValueT, std::size_t N>
view (std::array<ValueT,N> &rhs):
view (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::size (rhs))
{ ; }
///////////////////////////////////////////////////////////////////////
constexpr BeginT begin (void) noexcept { return m_begin; }
constexpr EndT end (void) noexcept { return m_end; }
constexpr BeginT begin (void) const noexcept { return m_begin; }
constexpr EndT end (void) const noexcept { return m_end; }
//---------------------------------------------------------------------
constexpr BeginT cbegin (void) const noexcept { return m_begin; }
constexpr EndT cend (void) const noexcept { return m_end; }
//---------------------------------------------------------------------
auto data (void) noexcept { return begin (); }
auto data (void) const noexcept { return begin (); }
//---------------------------------------------------------------------
auto& front (void) noexcept { return *m_begin; }
auto& front (void) const noexcept { return *m_begin; }
//---------------------------------------------------------------------
auto& back (void) noexcept { return *(m_end - 1); }
auto& back (void) const noexcept { return *(m_end - 1); }
///////////////////////////////////////////////////////////////////////
/// Returns true if the size of the view is zero.
constexpr bool
empty (void) const noexcept
{
return m_begin == m_end;
}
///--------------------------------------------------------------------
/// Returns true if the view is not empty; ie, there is data remaining.
constexpr operator bool () const noexcept
{
return not empty ();
}
///--------------------------------------------------------------------
/// Returns the number of items in the view.
constexpr auto
size (void) const noexcept
{
return static_cast<size_type> (std::distance (m_begin, m_end));
}
///--------------------------------------------------------------------
/// Returns a signed count of items in the view.
constexpr ssize_t
ssize (void) const noexcept
{
return std::distance (m_begin, m_end);
}
///--------------------------------------------------------------------
/// Returns a subview of the first `count` elements of this view.
[[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 };
};
///--------------------------------------------------------------------
/// Returns two subviews split at `pos`.
///
/// The first view extends from `begin` to `pos`, and the second view
/// extends from `pos` to `end`.
[[nodiscard]] constexpr std::pair<
view<BeginT,BeginT>,
view<BeginT,EndT>
>
split (BeginT pos) const
{
CHECK_GE (pos, m_begin);
CHECK_LE (pos, m_end );
return {
{ m_begin, pos },
{ pos, m_end }
};
}
///--------------------------------------------------------------------
template <
typename IndexT,
typename = std::enable_if_t<std::is_integral_v<IndexT>>
>
[[nodiscard]] constexpr auto
split (IndexT idx) const
{
CHECK_LE (cruft::cast::lossless<std::size_t> (idx), size ());
auto last = m_begin;
std::advance (last, idx);
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"
template <typename IndexA, typename IndexB>
[[nodiscard]] constexpr
auto
slice (IndexA a, IndexB b) const
{
CHECK_LIMIT (cruft::abs (a), IndexA {0}, cruft::cast::lossless<IndexA> (size ()));
CHECK_LIMIT (cruft::abs (b), IndexB {0}, cruft::cast::lossless<IndexB> (size ()));
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 view { first, last };
}
//---------------------------------------------------------------------
template <
typename IndexT,
typename = std::enable_if_t<std::is_integral_v<IndexT>>
>
[[nodiscard]] constexpr auto
head (IndexT idx) const
{
return std::get<0> (split (idx));
}
//---------------------------------------------------------------------
template <
typename IndexT,
typename = std::enable_if_t<std::is_integral_v<IndexT>>
>
[[nodiscard]] constexpr auto
tail (IndexT idx) const
{
return std::get<1> (split (idx));
}
//---------------------------------------------------------------------
template <
typename IndexT,
typename = std::enable_if_t<std::is_integral_v<IndexT>>
>
[[nodiscard]] constexpr auto
consume (IndexT count) const
{
auto [a,b] = split (count);
(void)a;
return b;
}
//---------------------------------------------------------------------
[[nodiscard]] constexpr view<BeginT,EndT>
consume (view<BeginT,EndT> prefix) const
{
assert (prefix.begin () == begin ());
assert (prefix.end () < end ());
return { prefix.end (), end () };
}
[[nodiscard]] constexpr view<BeginT,EndT>
consume (const BeginT pos) const
{
return { pos, end () };
}
///////////////////////////////////////////////////////////////////////
/// Explicitly cast to a view with different iterator types.
///
/// The source and destination iterator types must be:
/// * pointers
/// * alignable
///
/// It is undefined behaviour to cast with begin and/or end iterators
/// that do not have natural alignment. Instrumented builds _may_
/// provide diagnostics or assertions in this case.
///
/// \tparam ValueT The new iterator type
/// \return A view that uses the new iterator type
template <
typename ValueT,
typename = std::enable_if_t<
// We can only convert views that use pointer iterators
std::is_pointer_v<BeginT> &&
std::is_pointer_v<EndT> &&
std::is_same_v<BeginT,EndT> &&
std::is_pointer_v<ValueT>
>
>
view<ValueT>
cast (void) const
{
// The values they point to must allow for alignment in one
// direction or another.
//
// We prefer a static_assert over SFINAE because it reduces the
// header burden for users (they do not need to include the
// implementation of the pointer values to satisfy
// iterator_traits), and it is quite unlikely we want to disable
// this only if alignment is incompatible).
static_assert (
sizeof (typename std::iterator_traits<BeginT>::value_type) %
sizeof (typename std::iterator_traits<ValueT>::value_type) == 0 ||
sizeof (typename std::iterator_traits<ValueT>::value_type) %
sizeof (typename std::iterator_traits<BeginT>::value_type) == 0
);
return {
cast::alignment<ValueT> (m_begin),
cast::alignment<ValueT> (m_end)
};
}
///////////////////////////////////////////////////////////////////////
constexpr auto&&
operator[] (size_t idx) noexcept
{
return *std::next (begin (), idx);
}
//---------------------------------------------------------------------
constexpr auto&&
operator[] (size_t idx) const noexcept
{
return *std::next (begin (), idx);
}
private:
///////////////////////////////////////////////////////////////////////
BeginT m_begin;
EndT m_end;
};
//-------------------------------------------------------------------------
template <typename ValueT, std::size_t N>
view (ValueT(&)[N]) -> view<ValueT*,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>
>
>
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 ValueT, std::size_t N>
view (const std::array<ValueT,N>&) -> view<const ValueT*>;
template <typename ContainerT>
view (ContainerT&) -> view<
decltype (std::declval<ContainerT&> ().begin ()),
decltype (std::declval<ContainerT&> ().end ())
>;
template <typename ContainerT>
view (const ContainerT&) -> view<
decltype (std::declval<ContainerT const&> ().begin ()),
decltype (std::declval<ContainerT const&> ().end ())
>;
// base + count constructor
template <typename BeginT>
view (BeginT, std::uint64_t count) -> view<BeginT,BeginT>;
template <typename BeginT>
view (BeginT, std::uint32_t count) -> view<BeginT,BeginT>;
///////////////////////////////////////////////////////////////////////////
template <typename ValueT, size_t N>
auto
make_view (const ValueT (&arr)[N])
{
return view<const ValueT*> (arr + 0, arr + N);
}
//-------------------------------------------------------------------------
template <typename ContainerT>
auto
make_view (ContainerT &t)
{
return view { std::begin (t), std::end (t) };
}
//-------------------------------------------------------------------------
template <typename ContainerT>
auto
make_view (const ContainerT &t)
{
return view { 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 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 word 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...
///
/// We have to be careful that rval-references and other temporaries aren't
/// accepted in this signature.
template <
typename WordT = std::byte const,
typename T
>
cruft::view<WordT*>
make_byte_view (T &t)
{
static_assert (sizeof (T) % sizeof (WordT) == 0);
static_assert (std::is_const_v<T> ? std::is_const_v<WordT> : true);
return view {
cast::alignment<WordT*> (&t),
sizeof (T) / sizeof (WordT)
};
}
///////////////////////////////////////////////////////////////////////////
/// Returns a reference to a value of the designated type at the front of
/// the word-view. if there is insufficient data for the extraction an
/// exception will be thrown.
///
/// There are no validity or other checks performed on the returned data
/// this is deliberate, so that the function is safe to call on user
/// supplied data during parsing routines. it is up to the user to ensure
/// the object is valid.
///
/// The buffer object is advanced in place so that it no longer covers
/// the extract value
///
/// It is assumed the user has taken care of alignment concerns
template <
typename ValueT,
typename WordT,
// Only allow calls if the value is a multiple of the word size. It's
// useful to allow non-unit words for areas like TCP/IP which tend to
// operate on u16 words.
typename = std::enable_if_t<sizeof (ValueT) % sizeof (WordT) == 0>
>
ValueT const&
extract (view<WordT const*> &buffer)
{
if (unlikely (sizeof (ValueT) > buffer.size () * sizeof (WordT)))
throw std::runtime_error ("insufficient data for extraction");
auto const ptr = cast::alignment<ValueT const*> (buffer.data ());
buffer = buffer.consume (sizeof (ValueT) / sizeof (WordT));
return *ptr;
}
///////////////////////////////////////////////////////////////////////////
/// extracts an object of a specified type from the front of a byte-view.
///
/// in contrast to 'extract' this will always copy the bytes out from the
/// view, making the operation alignment safe.
template <
typename ValueT,
typename WordT,
typename = std::enable_if_t<sizeof (ValueT) % sizeof(WordT) == 0>
>
ValueT
read (view<WordT*> &buffer)
{
// We're going to use memcpy which requires that the type is
// trivially copyable.
static_assert (std::is_trivially_copyable_v<ValueT>);
if (unlikely (sizeof (ValueT) > buffer.size () * sizeof (WordT)))
throw std::runtime_error ("insufficient data for extraction");
std::aligned_storage_t<sizeof(ValueT),alignof(ValueT)> bytes;
memcpy (&bytes, buffer.data (), sizeof (ValueT));
buffer = buffer.consume (sizeof (ValueT) / sizeof (WordT));
return *reinterpret_cast<ValueT const*> (&bytes);
}
///////////////////////////////////////////////////////////////////////////
/// Tests whether an iterator falls within a given view.
template <typename IteratorT>
constexpr bool
intersects (view<IteratorT> a, IteratorT b)
{
return b >= a.begin () && b < a.end ();
}
///------------------------------------------------------------------------
/// Tests whether view `a` inclusively contains view `b`.
template <typename IteratorA, typename IteratorB>
constexpr bool
covers (
view<IteratorA,IteratorB> const &a,
view<IteratorA,IteratorB> const &b
) {
return a.begin () <= b.begin () && a.end () >= b.end ();
}
///////////////////////////////////////////////////////////////////////////
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 CharT>
bool
operator== (
view<const CharT*> lhs,
const std::basic_string<CharT> &rhs
) {
return lhs.size () == rhs.size () && std::equal (lhs.cbegin (), lhs.cend (), rhs.cbegin ());
}
inline bool
operator== (view<const char*> lhs, const char *rhs)
{
return lhs.size () == strlen (rhs) && std::equal (lhs.cbegin (), lhs.cend (), rhs);
}
///////////////////////////////////////////////////////////////////////////
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< (view<const char*> a, 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),
min (la, lb)
);
return res < 0 || (res == 0 && la < lb);
}
}
namespace cruft::debug {
///////////////////////////////////////////////////////////////////////////
template <typename IteratorT, typename ...ArgsT>
struct validator<
view<IteratorT>,
ArgsT&&...
> {
static bool
is_valid (view<IteratorT> data, ArgsT &&...args)
{
return std::all_of (
std::begin (data),
std::end (data),
[&] (auto const &i)
{
return ::cruft::debug::is_valid (i, args...);
});
}
};
};
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