[英]Template function dependent on non-type parameter
Is it somehow possible to define an overloaded template function based on a non-type parameter? 是否可以基于非类型参数定义重载模板函数?
following situation: 以下情况:
template<uint8_t> void SetupMem();
template<> void SetupMem<4>()
{ /* some code */ }
template<> void SetupMem<8>()
{ /* some code */ }
void TemplateCaller()
{
// use the plattform-specific template function at compile-time
SetupMem<sizeof(size_t)>();
}
now is it somehow possible to change the return value of SetupMem
based on the non-type parameter? 现在可以通过非类型参数更改SetupMem
的返回值吗? eg: 例如:
template<> uint32_t SetupMem<4>(){}
template<> uint64_t SetupMem<8>(){}
So that TemplateCaller()
does not explicitly calls SetupMem
with the desired template parameter (so avoiding something like: SetupMem<uint64, sizeof(size_t)>();
)? 这样, TemplateCaller()
不会使用所需的模板参数显式调用SetupMem
(因此避免类似: SetupMem<uint64, sizeof(size_t)>();
)吗? Possible solutions upto C++11 are welcome :) 欢迎使用C ++ 11之前的可能解决方案:)
You can write a type trait: 您可以编写类型特征:
template<::std::size_t x_Size> class
t_IntegralFromSize;
template<> class
t_IntegralFromSize<4> final
{
public: using type = ::std::uint32_t;
};
template<> class
t_IntegralFromSize<8> final
{
public: using type = ::std::uint64_t;
};
template<::std::size_t x_Size> typename t_IntegralFromSize<x_Size>::type
SetupMem();
template<> t_IntegralFromSize<4>::type
SetupMem<4>()
{ /* some code */ }
template<> t_IntegralFromSize<8>::type
SetupMem<8>()
{ /* some code */ }
void TemplateCaller()
{
// use the plattform-specific template function at compile-time
SetupMem<sizeof(size_t)>(); // works without changes
}
Just use simple function overloading and std::integral_constant
: 只需使用简单的函数重载和std::integral_constant
:
std::uint32_t SetupMem(std::integral_constant<int, 4>); // (0)
std::uint64_t SetupMem(std::integral_constant<int, 8>); // (1)
void TemplateCaller()
{
auto a = SetupMem(std::integral_constant<int, 4>{}); // calls (0)
auto b = SetupMem(std::integral_constant<int, 8>{}); // calls (1)
}
You can introduce a template type alias for readability: 您可以引入模板类型别名以提高可读性:
template <int X>
using ic = std::integral_constant<int, X>;
std::uint32_t SetupMem(ic<4>);
std::uint64_t SetupMem(ic<8>);
void TemplateCaller()
{
auto a = SetupMem(ic<4>{});
auto b = SetupMem(ic<8>{});
}
live example on wandbox.org wandbox.org上的实时示例
If your compiler doesn't support integral_constant
, all you need to do is define it yourself: 如果您的编译器不支持integral_constant
,那么您只需自己定义即可:
template <int>
struct ic { };
std::uint32_t SetupMem(ic<4>);
std::uint64_t SetupMem(ic<8>);
void TemplateCaller()
{
auto a = SetupMem(ic<4>{});
auto b = SetupMem(ic<8>{});
}
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