你可以抛出一个条件表达式？ （是：如何将边界检查扩展到多维？） [英] Can you throw within a conditional expression? (was: How can bounds-checking be extended to multiple dimensions?)
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问题描述
注意：我通过实现完全不同的解决了原始问题。
Note: I solved the original problem by realizing a completely different one. See the addendum for the new actual problem, but you can read the previous part for context.
这是我的一个扩展以前的帖子。我根据这个答案做了一个容器类：
This is an extension of one of my previous posts. I made a container class based on that answer:
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;
};
我试图在 c>。我想我会做一个版本的 slice ，它接受一个异常对象。与一般的 slice 不同，我的 checked_slice 必须接受一个内置的数组对象，因为指针和类类型与 operator [] ）没有（标准）方式给我bounds。
I'm trying to make a version of at for this container. I figured I'll just make a version of slice that takes an exception object. Unlike the general slice, my checked_slice has to take in a built-in array object, since pointers and class types (with operator []) don't have a (standard) way to give me bounds.
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 ）当我把它放入我的在：
(The remove_some_extents does what it says, instead of just one or all the C++11 standard library gives you.) When I put this into my 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 )...);
}
//...
};
我得到与数组到指针衰减相关的错误！ （我使用TDC-GCC 4.7.1，它与CodeBlocks 12.11 for Windows-8 Pro 32位捆绑在一起。）
I get errors related to array-to-pointer decay! (I'm using TDC-GCC 4.7.1 that's bundled with CodeBlocks 12.11 for Windows-8 Pro 32-bit.)
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]
我想使用数组引用取消数组到指针的衰减。这是一个GCC错误，还是我在某处搞砸了？
I thought using array references cancels array-to-pointer decay. Is this a GCC bug, or am I messing up somewhere?
对于slice.hpp，第141行第10列是函数的L-value版本） checked_slice 函数，而L142C1是函数的结尾括号。在array_md.hpp中，L284C112和L274C112是在函数， const 的返回非const。该列位于 static_cast 里面的i。
For "slice.hpp", Line 141, Col. 10 is the end of the statement in the (l-value version of) checked_slice function, while L142C1 is the function's ending bracket. In "array_md.hpp", L284C112 and L274C112 are return (and sole) statements of the at functions, const and non-const respectively. The column is at the "i" inside the static_cast.
顺便说一句， 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.
感谢。
：为 checked_slice 添加了基本案例和r值重载。
Added the base-case and r-value overloads for checked_slice.
附录：我有一些工作，但我不知道为什么旧的方式不工作。
Addendum: I got something that works, but I don't know why the old way didn't work.
我第一次注释掉r值重载对于 checked_slice ，以减少我必须使用的变量。然后我做了一个版本的 checked_slice ，适用于标准容器，但你不需要看到它，因为它没有帮助。
I first commented out the r-value overload for checked_slice, to reduce the variables I have to work with. I then made a version of checked_slice that works for standard containers, but you don't need to see it because it didn't help. (And I commented it out to make sure it didn't make a difference.)
我将常规版本更改为：
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)... );
}
我删除了实际测试和失败的部分，代码工作！这个问题似乎不是索引，但是抛出和/或条件！果然，当我改变为：
i.e. I removed the actual test and the throw-on-fail parts, and the code worked! The problem didn't seem to be the indexing, but the throw and/or conditional! Sure enough, when I changed it to:
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;
}
它仍然有效！什么给，我认为可以使用throw语句作为条件表达式的动作部分之一？这是我的编译器中的错误吗？
It still works! What gives, I thought it was OK to use a throw statement as one of the action parts of a conditional expression? Is it a bug in my compiler?
我可能不得不放弃和分离bounds-check到一个纯函数和throw-on-fail在
I may have to give up and separate the bounds-check to a pure-function and throw-on-fail within the at method.
推荐答案
因为我改变了这个问题，标记为一个新的。我在回答了重新询问另一个帖子，它工作。
Since I changed this question, it may have not been flagged as a new one. I got an answer from re-asking in another post, and it worked.
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