Примечание. Я решил исходную проблему, реализовав совершенно другую. См. приложение для новой актуальной проблемы, но вы можете прочитать предыдущую часть для контекста.
Это расширение одного из моих предыдущих постов. Я создал класс контейнера на основе этого ответа:
template < typename T, unsigned N0, unsigned ...N >
struct array_md
{
// There's a class template specialization with no extents.
// Imagine the various N... components are bracket-enclosed instead
// of comma-separated. And if "N..." is empty, then we just have "T"
// as the "direct_element_type". (I actually use recursive class
// definitions.)
using direct_element_type = T[N...];
using data_type = direct_element_type[ N0 ];
template < typename ...Indices >
auto operator ()( Indices &&...i )
noexcept( !indexing_result<data_type &, Indices...>::can_throw )
-> typename indexing_result<data_type &, Indices...>::type
{ return slice(data, static_cast<Indices &&>( i )...); }
template < typename ...Indices >
constexpr
auto operator ()( Indices &&...i ) const
noexcept( !indexing_result<data_type &, Indices...>::can_throw )
-> typename indexing_result<data_type &, Indices...>::type
{ return slice(data, static_cast<Indices &&>( i )...); }
data_type data;
};
Я пытаюсь сделать версию at для этого контейнера. Я решил просто сделать версию slice, которая принимает объект исключения. В отличие от общего slice, мой checked_slice должен принимать встроенный объект массива, поскольку указатели и типы классов (с operator []) не имеют (стандартного) способа дать мне границы.
template < typename E, typename T >
inline constexpr
auto checked_slice( E &&, T &&t ) noexcept -> T &&
{ return static_cast<T &&>(t); }
template < typename E, typename T, std::size_t N, typename ...V >
inline constexpr
auto checked_slice( E &&e, T (&t)[N], std::size_t u, V &&...v )
-> typename remove_some_extents<T[N], 1u + sizeof...(V)>::type &
{
return u < N ? checked_slice( static_cast<E &&>(e), static_cast<T &>(t[ u ]),
static_cast<V &&>(v)... ) : throw static_cast<E &&>( e );
}
template < typename E, typename T, std::size_t N, typename ...V >
inline constexpr
auto checked_slice( E &&e, T (&&t)[N], std::size_t u, V &&...v )
-> typename remove_some_extents<T[N], 1u + sizeof...(V)>::type &&
{
return u < N ? checked_slice( static_cast<E &&>(e),static_cast<T &&>(t[ u ]),
static_cast<V &&>(v)... ) : throw static_cast<E &&>( e );
}
(remove_some_extents делает то, что говорит, а не одну или всю стандартную библиотеку С++ 11, которую дает вам.) Когда я помещаю это в свой at:
template < typename T, unsigned N0, unsigned ...N >
struct array_md
{
//...
template < typename ...Indices >
auto at( Indices &&...i )
-> typename remove_some_extents<data_type, sizeof...( Indices )>::type &
{
return checked_slice(std::out_of_range{ "Index out of bounds" }, data,
static_cast<Indices &&>( i )...);
}
template < typename ...Indices >
constexpr
auto at( Indices &&...i ) const
-> typename remove_some_extents<data_type,sizeof...( Indices )>::type const &
{
return checked_slice(std::out_of_range{ "Index out of bounds" }, data,
static_cast<Indices &&>( i )...);
}
//...
};
Я получаю ошибки, связанные с распадом массива в указатель! (Я использую TDC-GCC 4.7.1, который поставляется вместе с CodeBlocks 12.11 для 32-разрядной версии Windows-8 Pro.)
In file included from container/array_md.hpp:36:0,
from test\arraymd_test.cpp:15:
utility/slice.hpp: In instantiation of 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = const int; unsigned int N = 2u; V = {}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = const int; std::size_t = unsigned int]':
container/array_md.hpp:284:112: required from 'constexpr const typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type& container::array_md<T, M, N ...>::at(Indices&& ...) const [with Indices = {int}; T = int; unsigned int M = 2u; unsigned int ...N = {}; typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type = int]'
test\arraymd_test.cpp:224:1: required from here
utility/slice.hpp:141:10: warning: returning reference to temporary [enabled by default]
utility/slice.hpp: In instantiation of 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = const char [2][6]; unsigned int N = 2u; V = {}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = const char [2][6]; std::size_t = unsigned int]':
container/array_md.hpp:284:112: required from 'constexpr const typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type& container::array_md<T, M, N ...>::at(Indices&& ...) const [with Indices = {int}; T = char [6]; unsigned int M = 2u; unsigned int ...N = {2u}; typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type = char [2][6]]'
test\arraymd_test.cpp:238:1: required from here
utility/slice.hpp:141:10: error: invalid initialization of reference of type 'const char (&)[2][6]' from expression of type 'const char (*)[6]'
utility/slice.hpp:142:1: error: body of constexpr function 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = const char [2][6]; unsigned int N = 2u; V = {}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = const char [2][6]; std::size_t = unsigned int]' not a return-statement
utility/slice.hpp: In instantiation of 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = const char [6]; unsigned int N = 2u; V = {}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = const char [6]; std::size_t = unsigned int]':
utility/slice.hpp:141:10: required from 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = const char [2][6]; unsigned int N = 2u; V = {int}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = const char [6]; std::size_t = unsigned int]'
container/array_md.hpp:284:112: required from 'constexpr const typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type& container::array_md<T, M, N ...>::at(Indices&& ...) const [with Indices = {int, int}; T = char [6]; unsigned int M = 2u; unsigned int ...N = {2u}; typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type = char [6]]'
test\arraymd_test.cpp:239:1: required from here
utility/slice.hpp:141:10: error: invalid initialization of reference of type 'const char (&)[6]' from expression of type 'const char*'
utility/slice.hpp:142:1: error: body of constexpr function 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = const char [6]; unsigned int N = 2u; V = {}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = const char [6]; std::size_t = unsigned int]' not a return-statement
utility/slice.hpp: In instantiation of 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = const char [2][6]; unsigned int N = 2u; V = {int}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = const char [6]; std::size_t = unsigned int]':
container/array_md.hpp:284:112: required from 'constexpr const typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type& container::array_md<T, M, N ...>::at(Indices&& ...) const [with Indices = {int, int}; T = char [6]; unsigned int M = 2u; unsigned int ...N = {2u}; typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type = char [6]]'
test\arraymd_test.cpp:239:1: required from here
utility/slice.hpp:141:10: error: invalid initialization of reference of type 'const char (&)[6]' from expression of type 'const char*'
utility/slice.hpp:142:1: error: body of constexpr function 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = const char [2][6]; unsigned int N = 2u; V = {int}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = const char [6]; std::size_t = unsigned int]' not a return-statement
utility/slice.hpp: In instantiation of 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = const char [2][6]; unsigned int N = 2u; V = {unsigned int}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = const char [6]; std::size_t = unsigned int]':
container/array_md.hpp:284:112: required from 'constexpr const typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type& container::array_md<T, M, N ...>::at(Indices&& ...) const [with Indices = {int, unsigned int}; T = char [6]; unsigned int M = 2u; unsigned int ...N = {2u}; typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type = char [6]]'
test\arraymd_test.cpp:261:5: required from here
utility/slice.hpp:141:10: error: invalid initialization of reference of type 'const char (&)[6]' from expression of type 'const char*'
utility/slice.hpp:142:1: error: body of constexpr function 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = const char [2][6]; unsigned int N = 2u; V = {unsigned int}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = const char [6]; std::size_t = unsigned int]' not a return-statement
utility/slice.hpp: In instantiation of 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = int; unsigned int N = 2u; V = {}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = int; std::size_t = unsigned int]':
container/array_md.hpp:274:112: required from 'typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type& container::array_md<T, M, N ...>::at(Indices&& ...) [with Indices = {int}; T = int; unsigned int M = 2u; unsigned int ...N = {}; typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type = int]'
test\arraymd_test.cpp:220:1: required from here
utility/slice.hpp:141:10: error: invalid initialization of non-const reference of type 'remove_some_extents<int [2], 1u>::type& {aka int&}' from an rvalue of type 'int'
utility/slice.hpp:142:1: error: body of constexpr function 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = int; unsigned int N = 2u; V = {}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = int; std::size_t = unsigned int]' not a return-statement
utility/slice.hpp: In instantiation of 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = char [2][6]; unsigned int N = 2u; V = {}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = char [2][6]; std::size_t = unsigned int]':
container/array_md.hpp:274:112: required from 'typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type& container::array_md<T, M, N ...>::at(Indices&& ...) [with Indices = {int}; T = char [6]; unsigned int M = 2u; unsigned int ...N = {2u}; typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type = char [2][6]]'
test\arraymd_test.cpp:234:1: required from here
utility/slice.hpp:141:10: error: invalid initialization of non-const reference of type 'char (&)[2][6]' from an rvalue of type 'char (*)[6]'
utility/slice.hpp:142:1: error: body of constexpr function 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = char [2][6]; unsigned int N = 2u; V = {}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = char [2][6]; std::size_t = unsigned int]' not a return-statement
utility/slice.hpp: In instantiation of 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = char [6]; unsigned int N = 2u; V = {}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = char [6]; std::size_t = unsigned int]':
utility/slice.hpp:141:10: required from 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = char [2][6]; unsigned int N = 2u; V = {int}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = char [6]; std::size_t = unsigned int]'
container/array_md.hpp:274:112: required from 'typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type& container::array_md<T, M, N ...>::at(Indices&& ...) [with Indices = {int, int}; T = char [6]; unsigned int M = 2u; unsigned int ...N = {2u}; typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type = char [6]]'
test\arraymd_test.cpp:235:1: required from here
utility/slice.hpp:141:10: error: invalid initialization of non-const reference of type 'char (&)[6]' from an rvalue of type 'char*'
utility/slice.hpp:142:1: error: body of constexpr function 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = char [6]; unsigned int N = 2u; V = {}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = char [6]; std::size_t = unsigned int]' not a return-statement
utility/slice.hpp: In instantiation of 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = char [2][6]; unsigned int N = 2u; V = {int}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = char [6]; std::size_t = unsigned int]':
container/array_md.hpp:274:112: required from 'typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type& container::array_md<T, M, N ...>::at(Indices&& ...) [with Indices = {int, int}; T = char [6]; unsigned int M = 2u; unsigned int ...N = {2u}; typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type = char [6]]'
test\arraymd_test.cpp:235:1: required from here
utility/slice.hpp:141:10: error: invalid initialization of non-const reference of type 'char (&)[6]' from an rvalue of type 'char*'
utility/slice.hpp:142:1: error: body of constexpr function 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = char [2][6]; unsigned int N = 2u; V = {int}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = char [6]; std::size_t = unsigned int]' not a return-statement
utility/slice.hpp: In instantiation of 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = char [2][6]; unsigned int N = 2u; V = {long double}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = char [6]; std::size_t = unsigned int]':
container/array_md.hpp:274:112: required from 'typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type& container::array_md<T, M, N ...>::at(Indices&& ...) [with Indices = {int, long double}; T = char [6]; unsigned int M = 2u; unsigned int ...N = {2u}; typename remove_some_extents<typename container::array_md<T, N ...>::data_type [M], sizeof (Indices ...)>::type = char [6]]'
test\arraymd_test.cpp:260:5: required from here
utility/slice.hpp:141:10: error: invalid initialization of non-const reference of type 'char (&)[6]' from an rvalue of type 'char*'
utility/slice.hpp:142:1: error: body of constexpr function 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = char [2][6]; unsigned int N = 2u; V = {long double}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = char [6]; std::size_t = unsigned int]' not a return-statement
utility/slice.hpp: In function 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = const char [2][6]; unsigned int N = 2u; V = {unsigned int}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = const char [6]; std::size_t = unsigned int]':
utility/slice.hpp:142:1: warning: control reaches end of non-void function [-Wreturn-type]
utility/slice.hpp: In function 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = const char [2][6]; unsigned int N = 2u; V = {int}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = const char [6]; std::size_t = unsigned int]':
utility/slice.hpp:142:1: warning: control reaches end of non-void function [-Wreturn-type]
utility/slice.hpp: In function 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = const char [6]; unsigned int N = 2u; V = {}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = const char [6]; std::size_t = unsigned int]':
utility/slice.hpp:142:1: warning: control reaches end of non-void function [-Wreturn-type]
utility/slice.hpp: In function 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = const char [2][6]; unsigned int N = 2u; V = {}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = const char [2][6]; std::size_t = unsigned int]':
utility/slice.hpp:142:1: warning: control reaches end of non-void function [-Wreturn-type]
utility/slice.hpp: In function 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = char [2][6]; unsigned int N = 2u; V = {long double}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = char [6]; std::size_t = unsigned int]':
utility/slice.hpp:142:1: warning: control reaches end of non-void function [-Wreturn-type]
utility/slice.hpp: In function 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = char [2][6]; unsigned int N = 2u; V = {int}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = char [6]; std::size_t = unsigned int]':
utility/slice.hpp:142:1: warning: control reaches end of non-void function [-Wreturn-type]
utility/slice.hpp: In function 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = char [6]; unsigned int N = 2u; V = {}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = char [6]; std::size_t = unsigned int]':
utility/slice.hpp:142:1: warning: control reaches end of non-void function [-Wreturn-type]
utility/slice.hpp: In function 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = char [2][6]; unsigned int N = 2u; V = {}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = char [2][6]; std::size_t = unsigned int]':
utility/slice.hpp:142:1: warning: control reaches end of non-void function [-Wreturn-type]
utility/slice.hpp: In function 'constexpr typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type& checked_slice(E&&, T (&)[N], std::size_t, V&& ...) [with E = std::out_of_range; T = int; unsigned int N = 2u; V = {}; typename remove_some_extents<T [N], (1u + sizeof (V ...))>::type = int; std::size_t = unsigned int]':
utility/slice.hpp:142:1: warning: control reaches end of non-void function [-Wreturn-type]
Я думал, что использование ссылок на массив отменяет распад массива на указатель. Это ошибка GCC или я где-то ошибся?
Для «slice.hpp» строка 141, столбец 10 — это конец оператора в (версии с l-значением) checked_slice, а L142C1 — это закрывающая квадратная скобка функции. В «array_md.hpp» L284C112 и L274C112 являются возвращаемыми (и единственными) операторами функций at, const и неконстантными соответственно. Столбец находится в «i» внутри static_cast.
Кстати, вот remove_some_extents:
// Forward declaration
template < typename Array, std::size_t Count >
struct remove_some_extents;
// Case with indefinite array but no extents to strip
template < typename T >
struct remove_some_extents< T[], 0u >
{ typedef T type[]; };
// Case with definite array but no extents to strip
template < typename T, std::size_t N >
struct remove_some_extents< T[N], 0u >
{ typedef T type[N]; };
// Case with non-array type but no extents to strip
template < typename T >
struct remove_some_extents< T, 0u >
{ typedef T type; };
// Case with indefinite array and extents to strip
template < typename T, std::size_t L >
struct remove_some_extents< T[], L >
{ typedef typename remove_some_extents<T, L - 1u>::type type; };
// Case with definite array and extents to strip
template < typename T, std::size_t N, std::size_t L >
struct remove_some_extents< T[N], L >
{ typedef typename remove_some_extents<T, L - 1u>::type type; };
// Right now, non-array type with non-zero strip count should give an error.
Спасибо.
Изменить: добавлены перегрузки base-case и r-value для checked_slice.
Дополнение: у меня есть кое-что, что работает, но я не знаю, почему старый способ не работал.
Сначала я закомментировал перегрузку r-значения для checked_slice, чтобы уменьшить количество переменных, с которыми мне приходится работать. Затем я сделал версию checked_slice, которая работает для стандартных контейнеров, но вам не нужно ее видеть, потому что это не помогло. (И я закомментировал это, чтобы убедиться, что это не имеет значения.)
Я изменил обычную версию на:
template < typename E, typename T, std::size_t N, typename ...V >
inline constexpr
auto checked_slice( E &&e, T (&t)[N], std::size_t u, V &&...v )
-> typename remove_some_extents<T[N], 1u + sizeof...(V)>::type &
{
return checked_slice( static_cast<E &&>(e), static_cast<T &>(t[ u ]),
static_cast<V &&>(v)... );
}
т. е. я удалил фактический тест и части, вызывающие отказ, и код заработал! Проблема оказалась не в индексации, а в броске и/или условном! Конечно же, когда я изменил его на:
template < typename E, typename T, std::size_t N, typename ...V >
inline
auto checked_slice( E &&e, T (&t)[N], std::size_t u, V &&...v )
-> typename remove_some_extents<T[N], 1u + sizeof...(V)>::type &
{
if ( u < N )
return checked_slice(static_cast<E &&>(e),t[u],static_cast<V &&>(v)...);
else
throw e;
}
Он все еще работает! Что дает, я думал, что можно использовать оператор throw в качестве одной из частей действия условного выражения? Это ошибка в моем компиляторе?
Возможно, мне придется отказаться и разделить проверку границ на чистую функцию и бросок при сбое в методе at.
