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Back to General and Gameplay Programming

Partial template specialization

Started by
6 comments, last by Misery 11 years, 12 months ago
Hello,

I am trying to create a matrix template class. I would like Sum() function to act differently for bool types. What I need to make it elegant class is partial template specialization. How do I do it?



template <class DATA,class INT_TYPE>
class TMatrix
{
private:
DATA *d;
INT_TYPE rows,cols;

public:
DATA Sum(); //count the sum of element
// for bool data type I would like to get:
INT_TYPE Sum(); //counts the number of elements that are true, so it cannot return bool, but INT_TYPE instead
}



And how do I create definition of such function outside the class?

Thanks in advance,
Regards,
Misery
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You could do something like this:

template<typename T>
struct sum_traits;

template<typename T>
class matrix {
public:
typedef typename sum_traits<T>::sum_type sum_type;

sum_type sum() const;
};

The nice thing about this is that it is general - the sum_type for char/short should probably be longer than the data type itself - at least a full int if not a long.

Example:


#include <vector>
#include <cstdlib>
#include <iostream>

template<typename T>
struct sum_traits;

template<typename T>
class example {
public:
void add(T item) {
data.push_back(item);
}

typedef typename sum_traits<T>::sum_type sum_type;

sum_type sum() const {
sum_type result = 0;
for(int i = 0 ; i < data.size() ; ++i) {
result += data;
}
return result;
}

private:
std::vector<T> data;
};

template<>
struct sum_traits<int> {
typedef long sum_type;
};

template<>
struct sum_traits<bool> {
typedef int sum_type;
};

int main() {
example<int> a;
for(int i = 0 ; i < 10 ; ++i ) {
a.add(std::rand());
}
a.add(0xffffff00);

std::cout << "Sum<int>: " << a.sum() << '\n';

example<bool> b;
for(int i = 0 ; i < 10000 ; ++i) {
b.add(std::rand() > (RAND_MAX / 2));
}
std::cout << "Sum<bool>: " << b.sum() << '\n';
}
blog | twitter
It looks qute nice, but i would like to use usual template specialization in manner like:

template <class INT_TYPE>
INT_TYPE Matrix<bool,INT_TYPE>::Sum()
{
//sum all true elements
}


How doI do that? My compiler always returnsan error saying that this function template requires two elements.
You can't specialize individual member functions of a template class without specializing the entire class.
Thanks, so I'll find something else :]
A somewhat cheap trick to get around "specialize the whole class" thing is to create a helper class that only contains the sum functionality and inherit from that, that way you only have to specialize that one. The other way around works too obviously put the non special functionality into a base class and only specialize classes that inherit from it.
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Well, thinking on this again, the simpler solution that might suffice is default template arguments:


#include <vector>
#include <cstdlib>
#include <iostream>

template <typename type, typename size_type, typename sum_type = type>
class example
{
public:
sum_type sum() const {
sum_type result = 0;
for(int i = 0 ; i < data.size() ; ++i) {
result += data;
}
return result;
}

void add(type item) {
data.push_back(item);
}


private:
std::vector<type> data;
};

int main() {
example<int> a;
for(int i = 0 ; i < 10 ; ++i ) {
a.add(std::rand());
}
a.add(0xffffff00);

std::cout << "Sum<int>: " << a.sum() << '\n';

example<bool> b;
for(int i = 0 ; i < 10000 ; ++i) {
b.add(std::rand() > (RAND_MAX / 2));
}
std::cout << "Sum<bool>: " << b.sum() << '\n';
}

You can now create a typedef for bool_matrix as something like matrix<bool, size_t, size_t>.
blog | twitter
Actually, at last I decided to derive BoolMatrix class from Matrix class. The main problem I was trying to work around was that I wanted to use BoolMatrix argument in one of the Matrix methods. And the second problem was that I needed to make it possible to change the INT_TYPE used to matrix indexing, because in MSVC OpenMP works only on signed long int and I also use GCC and Intel Compiler.
Anyway, as always, thanks to You Guys I have tested a few very clever solutions and achieved the goal.
Thanks and regards biggrin.png

This topic is closed to new replies.

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