Note:我通过实现一个完全不同的问题来解决最初的问题。有关新的实际问题，请参阅附录，但您可以阅读前一部分以了解上下文。
这是我的一个的扩展以前的帖子 https://stackoverflow.com/q/10171525/1010226。我根据这个答案创建了一个容器类：
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;
};
我正在尝试制作一个版本at对于这个容器。我想我只会制作一个版本slice需要一个异常对象。与一般的不同slice, my checked_slice必须接受内置数组对象，因为指针和类类型（带有operator []）没有（标准）方法给我界限。
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 );
}
(The remove_some_extents按照它所说的去做，而不是仅仅 C++11 标准库为您提供的一个或全部。）当我将其放入我的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 )...);
}
//...
};
我收到与数组到指针衰减相关的错误！ （我使用的是 TDC-GCC 4.7.1，它与适用于 Windows-8 Pro 32 位的 CodeBlocks 12.11 捆绑在一起。）
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]
我认为使用数组引用可以取消数组到指针的衰减。这是 GCC 错误，还是我在某个地方搞砸了？
对于“slice.hpp”，第 141 行第 10 列是（左值版本）中语句的结尾checked_slice函数，而 L142C1 是函数的结束括号。在“array_md.hpp”中，L284C112 和 L274C112 是返回（也是唯一）语句at功能，const和非常量分别。该列位于“i”内static_cast.
顺便说一下，这里是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.
Thanks.
Edit:添加了基本情况和右值重载checked_slice.
附录：我得到了一些有用的东西，但我不知道为什么旧方法不起作用。
我首先注释掉了 r 值过载checked_slice，以减少我必须处理的变量。然后我做了一个版本checked_slice这适用于标准容器，但您不需要看到它，因为它没有帮助。 （我将其注释掉以确保它不会产生影响。）
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)... );
}
即，我删除了实际测试和失败时抛出的部分，并且代码有效！问题似乎不是索引，而是抛出和/或条件！果然，当我把它改成：
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！是什么让我认为可以使用 throw 语句作为条件表达式的操作部分之一？这是我的编译器中的错误吗？
我可能不得不放弃并将边界检查分离为纯函数并在失败时抛出at method.
