在已经具有模板变量的函数中传递可变参数 [英] Passing variadic parameters in an already template-variadic function
问题描述
标题不好,但我想不出更好的办法。随时更改它。
这里是我目前正在研究的模板多维数组类。我正在尝试尽可能地优化它:
#include< array>
模板< typename T,std :: size_t ...尺寸>
class multidimensional_array
{
public:
使用value_type = T;
使用size_type = std :: size_t;
私人:
template< typename = void>
static constexpr size_type乘法(无效)
{
return 1u;
}
template< std :: size_t首先,std :: size_t ... Other>
static constexpr size_type乘法(无效)
{
return First * multiDimension_array :: multiply< Other ...>();
}
public:
使用container_type = std :: array< value_type,multidimensional_array :: multiply< Dimensions ...>()> ;;
使用reference = value_type& ;;
使用const_reference = value_type const& ;;
使用迭代器=类型名container_type :: iterator;
私有:
container_type m_data_array;
template< typename = void>
static constexpr size_type linearise(void)
{
返回0u;
}
template< std :: size_t首先,std :: size_t ... Other>
静态constexpr size_type线性化(std :: size_t索引,std :: size_t索引...)
{
返回multiDimension_array :: multiply< Other ...>()* index + multiDimension_array :: linearise< Other ...>(索引);
}
public:
//构造函数
显式multiDimension_array(const_reference value = value_type {})
{
multiDimension_array :: fill(值);
}
//访问器
参考operator()(std :: size_t索引...)
{
return m_data_array [multiple_array :: linearise< ; Dimensions ...>(indexes)];
}
const_reference operator()(std :: size_tindex ...)const
{
return m_data_array [multiple_array :: linearise< Dimensions ...> ;(indexs)];
}
//迭代器
迭代器begin()
{
return m_data_array.begin();
}
迭代器end()
{
return m_data_array.end();
}
//其他
void fill(const_reference value)
{
m_data_array.fill(value);
}
};
我的主要功能是
int main(void)
{
multiDimension_array< int,2u,3u,4u,5u,6u> foo;
int k = 0;
for(auto& s:foo)
s = k ++;
// std :: cout<< foo(0u,0u,0u,1u,0u)<< std :: endl;
返回0;
}
以上代码编译器无警告/错误。但是,一旦我取消注释 std :: cout
部分,我就会得到:
g ++-7 -std = c ++ 17 -o foo.o -c foo.cpp -Wall -Wextra -pedantic
foo.cpp:在'multidimensional_array< T,Dimensions>'的实例中:: value_type&多维数组< T,尺寸> :: operator()(std :: size_t,...)[with T = int; long unsigned int ... Dimensions = {2,3,4,5,6};多维数组< T,尺寸> :: reference = int& ;;多维数组< T,维度> :: value_type = int; std :: size_t = long unsigned int]':
foo.cpp:99:37:从此处需要
foo.cpp:60:72:错误:没有匹配的函数来调用 multiarray_array< int 、、 2、3、4、5、6> :: linearise< 2、3、4、5、6>(std :: size_t&)'
返回m_data_array [multiple_array :: linearise< Dimensions ...> ;(indexs)];
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ ^ ~~~~~~~~
foo.cpp:38:30:注意:候选人:template< class>静态constexpr多维数组< T,尺寸> :: size_type多维数组< T,尺寸> :: linearise()[具有< template-parameter-2-1> =< template-parameter-1-1> ;; T = int; long unsigned int ... Dimensions = {2,3,4,5,6}]
静态constexpr size_type linearise(void)
^ ~~~~~~~~
foo。 cpp:38:30:注意:模板参数推导/替换失败:
foo.cpp:60:72:错误:模板参数的数量错误(5,应至少为0)
return m_data_array [ multiDimension_array :: linearise< Dimensions ...>(indexes)];
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ ^ ~~~~~~~~
foo.cpp:44:30:注意:候选人:template< long unsigned int首先,long unsigned int ... Other>静态常量表达式multiDimension_array< T,Dimensions> :: size_type multiDimension_array< T,Dimensions> :: linearise(std :: size_t,std :: size_t,...)[具有长无符号int First = First; long unsigned int ... Other = {Other ...}; T = int; long unsigned int ... Dimensions = {2,3,4,5,6}]
静态constexpr size_type linearise(std :: size_t索引,std :: size_t索引...)
^〜 ~~~~~~~
foo.cpp:44:30:注意:模板参数推导/替换失败:
foo.cpp:60:72:注意:候选人期望2个参数,其中1个提供了
return m_data_array [multimedia_array :: linearise< Dimensions ...>(indexes)];
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ ^ ~~~~~~~~
Makefile:17:目标'foo.o'的配方失败
make:*** [foo.o]错误1
我知道现在为什么。我的问题是,如何解决 linearise
以便它可以通过 indexs
而不通过 va_list
等等?不幸的是 linearise
已经是一个模板,可变参数函数,因此在这方面我不能使用可变参数模板恶作剧。
如前面的问题问题是以下签名
template< std :: size_t首先,std :: size_t ...其他>
静态constexpr size_type线性化(std :: size_t索引,
std :: size_t索引...)
参考运算符()(std :: size_t索引...)
const_reference运算符()(std :: size_t索引...)const
不是什么意思( indexes
std :: size_t
的可变列表),但完全等效
template< std :: size_t首先,std :: size_t ...其他>
静态constexpr size_type线性化(std :: size_t索引,
std :: size_t索引,
...)
参考运算符()(std :: size_t索引,...)
const_reference运算符()(std :: size_t索引,...)const
其中,索引
是单个 std :: size_t
,后跟C样式
一个简单的解决方案(您标记了C ++ 17,但从C ++ 11开始可用)是基于可变参数模板的使用。 / p>
例如,如下所示
template< std :: size_t首先,std :: size_t ...其他,类型名... Ts>
静态constexpr size_type线性化(std :: size_t索引,
Ts ...索引)
{return multiDimension_array :: multiply< Other ...>()*索引
+ multiDimension_array :: linearise< Other ...>(索引...); }
//访问器
模板< typename ... Ts>
参考operator()(Ts ...索引)
{return m_data_array [
multiDimension_array :: linearise< Dimensions ...>(indexes ...)]; }
模板< typename ... Ts>
const_reference operator()(Ts ...索引)const
{return m_data_array [
multiDimension_array :: linearise< Dimensions ...>(indexes ...)]; }
以下是您的代码,已修改且可编译
#include< array>
#include< iostream>
模板< typename T,std :: size_t ... Dimensions>
class multidimensional_array
{
public:
using value_type = T;
使用size_type = std :: size_t;
私人:
模板< typename = void>
static constexpr size_type乘法()
{return 1u; }
模板< std :: size_t首先,std :: size_t ... Other>
静态constexpr size_type乘法(无效)
{return First * multiDimension_array :: multiply< Other ...>(); }
public:
使用container_type = std :: array< value_type,
multiDimension_array :: multiply< Dimensions ...>()> ;;
使用reference = value_type& ;;
使用const_reference = value_type const& ;;
使用迭代器=类型名container_type :: iterator;
私人:
container_type m_data_array;
模板< typename = void>
static constexpr size_type linearise()
{return 0u; }
模板< std :: size_t首先,std :: size_t ...其他,类型名称... Ts>
静态constexpr size_type线性化(std :: size_t索引,
Ts ...索引)
{return multiDimension_array :: multiply< Other ...>()*索引
+ multiDimension_array :: linearise< Other ...>(索引...); }
public:
//构造函数
显式multiDimension_array(const_reference value = value_type {})
{multiDimension_array :: fill(value); }
//访问器
模板< typename ... Ts>
参考operator()(Ts ...索引)
{return m_data_array [
multiDimension_array :: linearise< Dimensions ...>(indexes ...)]; }
模板< typename ... Ts>
const_reference operator()(Ts ...索引)const
{return m_data_array [
multiDimension_array :: linearise< Dimensions ...>(indexes ...)]; }
//迭代器
迭代器begin()
{return m_data_array.begin(); }
迭代器end()
{return m_data_array.end(); }
//其他
无效填充(const_reference值)
{m_data_array.fill(value); }
};
int main()
{
multiDimension_array< int,2u,3u,4u,5u,6u> foo;
int k {0};
for(auto& s:foo)
s = k ++;
std :: cout<< foo(0u,0u,0u,1u,0u)<< std :: endl;
}
奖金建议。
您标记了C ++ 17,因此可以使用折叠。
因此,您可以替换成对的 multiply()
模板函数
模板< typename = void>
static constexpr size_type乘法()
{return 1u; }
模板< std :: size_t首先,std :: size_t ... Other>
静态constexpr size_type乘法()
{return First * multiDimension_array :: multiply< Other ...>(); }
有一个折叠的
模板< std :: size_t ... Sizes>
静态constexpr size_type乘法()
{return(1U * ... * Sizes); }
The title is bad but I couldn't come up with anything better. Feel free to change it.
Here's a template multidimensional array class that I'm currently working on. I'm trying to optimise it as much as I can:
#include <array>
template <typename T, std::size_t... Dimensions>
class multidimensional_array
{
public:
using value_type = T;
using size_type = std::size_t;
private:
template<typename = void>
static constexpr size_type multiply(void)
{
return 1u;
}
template<std::size_t First, std::size_t... Other>
static constexpr size_type multiply(void)
{
return First * multidimensional_array::multiply<Other...>();
}
public:
using container_type = std::array<value_type, multidimensional_array::multiply<Dimensions...>()>;
using reference = value_type &;
using const_reference = value_type const&;
using iterator = typename container_type::iterator;
private:
container_type m_data_array;
template<typename = void>
static constexpr size_type linearise(void)
{
return 0u;
}
template<std::size_t First, std::size_t... Other>
static constexpr size_type linearise(std::size_t index, std::size_t indexes...)
{
return multidimensional_array::multiply<Other...>()*index + multidimensional_array::linearise<Other...>(indexes);
}
public:
// Constructor
explicit multidimensional_array(const_reference value = value_type {})
{
multidimensional_array::fill(value);
}
// Accessors
reference operator()(std::size_t indexes...)
{
return m_data_array[multidimensional_array::linearise<Dimensions...>(indexes)];
}
const_reference operator()(std::size_t indexes...) const
{
return m_data_array[multidimensional_array::linearise<Dimensions...>(indexes)];
}
// Iterators
iterator begin()
{
return m_data_array.begin();
}
iterator end()
{
return m_data_array.end();
}
// Other
void fill(const_reference value)
{
m_data_array.fill(value);
}
};
My main function is
int main(void)
{
multidimensional_array<int, 2u, 3u, 4u, 5u, 6u> foo;
int k = 0;
for (auto& s : foo)
s = k++;
//std::cout << foo(0u, 0u, 0u, 1u, 0u) << std::endl;
return 0;
}
The above code compilers without warning/error. As soon as I uncomment the std::cout
part though, I get this:
g++-7 -std=c++17 -o foo.o -c foo.cpp -Wall -Wextra -pedantic
foo.cpp: In instantiation of ‘multidimensional_array<T, Dimensions>::value_type& multidimensional_array<T, Dimensions>::operator()(std::size_t, ...) [with T = int; long unsigned int ...Dimensions = {2, 3, 4, 5, 6}; multidimensional_array<T, Dimensions>::reference = int&; multidimensional_array<T, Dimensions>::value_type = int; std::size_t = long unsigned int]’:
foo.cpp:99:37: required from here
foo.cpp:60:72: error: no matching function for call to ‘multidimensional_array<int, 2, 3, 4, 5, 6>::linearise<2, 3, 4, 5, 6>(std::size_t&)’
return m_data_array[multidimensional_array::linearise<Dimensions...>(indexes)];
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~
foo.cpp:38:30: note: candidate: template<class> static constexpr multidimensional_array<T, Dimensions>::size_type multidimensional_array<T, Dimensions>::linearise() [with <template-parameter-2-1> = <template-parameter-1-1>; T = int; long unsigned int ...Dimensions = {2, 3, 4, 5, 6}]
static constexpr size_type linearise(void)
^~~~~~~~~
foo.cpp:38:30: note: template argument deduction/substitution failed:
foo.cpp:60:72: error: wrong number of template arguments (5, should be at least 0)
return m_data_array[multidimensional_array::linearise<Dimensions...>(indexes)];
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~
foo.cpp:44:30: note: candidate: template<long unsigned int First, long unsigned int ...Other> static constexpr multidimensional_array<T, Dimensions>::size_type multidimensional_array<T, Dimensions>::linearise(std::size_t, std::size_t, ...) [with long unsigned int First = First; long unsigned int ...Other = {Other ...}; T = int; long unsigned int ...Dimensions = {2, 3, 4, 5, 6}]
static constexpr size_type linearise(std::size_t index, std::size_t indexes...)
^~~~~~~~~
foo.cpp:44:30: note: template argument deduction/substitution failed:
foo.cpp:60:72: note: candidate expects 2 arguments, 1 provided
return m_data_array[multidimensional_array::linearise<Dimensions...>(indexes)];
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~
Makefile:17: recipe for target 'foo.o' failed
make: *** [foo.o] Error 1
And I know why now. My question is, how can I fix linearise
so that it can pass indexes
without going through va_list
and such? Unfortunately linearise
is already a template, variadic function, so I can't use variadic template shenanigans in that regard.
As in preceding question the problem is that the following signatures
template<std::size_t First, std::size_t... Other>
static constexpr size_type linearise(std::size_t index,
std::size_t indexes...)
reference operator()(std::size_t indexes...)
const_reference operator()(std::size_t indexes...) const
aren't what do you mean (indexes
a variadic list of std::size_t
) but are exactly equivalent to
template<std::size_t First, std::size_t... Other>
static constexpr size_type linearise(std::size_t index,
std::size_t indexes,
...)
reference operator()(std::size_t indexes, ...)
const_reference operator()(std::size_t indexes, ...) const
where indexes
is a single std::size_t
followed by a C-style optional sequence of argument.
A simple solution (you tagged C++17 but is available starting from C++11) is based on the use of variadic templates.
By example, as follows
template <std::size_t First, std::size_t ... Other, typename ... Ts>
static constexpr size_type linearise (std::size_t index,
Ts ... indexes)
{ return multidimensional_array::multiply<Other...>() * index
+ multidimensional_array::linearise<Other...>(indexes...); }
// Accessors
template <typename ... Ts>
reference operator() (Ts ... indexes)
{ return m_data_array[
multidimensional_array::linearise<Dimensions...>(indexes...)]; }
template <typename ... Ts>
const_reference operator() (Ts ... indexes) const
{ return m_data_array[
multidimensional_array::linearise<Dimensions...>(indexes...)]; }
The following is you're code, modified and compilable
#include <array>
#include <iostream>
template <typename T, std::size_t ... Dimensions>
class multidimensional_array
{
public:
using value_type = T;
using size_type = std::size_t;
private:
template <typename = void>
static constexpr size_type multiply ()
{ return 1u; }
template <std::size_t First, std::size_t ... Other>
static constexpr size_type multiply(void)
{ return First * multidimensional_array::multiply<Other...>(); }
public:
using container_type = std::array<value_type,
multidimensional_array::multiply<Dimensions...>()>;
using reference = value_type &;
using const_reference = value_type const &;
using iterator = typename container_type::iterator;
private:
container_type m_data_array;
template <typename = void>
static constexpr size_type linearise ()
{ return 0u; }
template <std::size_t First, std::size_t ... Other, typename ... Ts>
static constexpr size_type linearise (std::size_t index,
Ts ... indexes)
{ return multidimensional_array::multiply<Other...>() * index
+ multidimensional_array::linearise<Other...>(indexes...); }
public:
// Constructor
explicit multidimensional_array (const_reference value = value_type{})
{ multidimensional_array::fill(value); }
// Accessors
template <typename ... Ts>
reference operator() (Ts ... indexes)
{ return m_data_array[
multidimensional_array::linearise<Dimensions...>(indexes...)]; }
template <typename ... Ts>
const_reference operator() (Ts ... indexes) const
{ return m_data_array[
multidimensional_array::linearise<Dimensions...>(indexes...)]; }
// Iterators
iterator begin ()
{ return m_data_array.begin(); }
iterator end ()
{ return m_data_array.end(); }
// Other
void fill (const_reference value)
{ m_data_array.fill(value); }
};
int main ()
{
multidimensional_array<int, 2u, 3u, 4u, 5u, 6u> foo;
int k{ 0 };
for ( auto & s : foo )
s = k++;
std::cout << foo(0u, 0u, 0u, 1u, 0u) << std::endl;
}
Bonus suggestion.
You tagged C++17 so you can use "folding".
So you can substitute the couple of multiply()
template functions
template <typename = void>
static constexpr size_type multiply ()
{ return 1u; }
template <std::size_t First, std::size_t ... Other>
static constexpr size_type multiply ()
{ return First * multidimensional_array::multiply<Other...>(); }
with a single folded one
template <std::size_t ... Sizes>
static constexpr size_type multiply ()
{ return ( 1U * ... * Sizes ); }
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