If we want to define a different implementation for a template when a
specific type is passed as template parameter, we can declare a
specialization of that template.
For example, let's suppose that we have a very simple class called
mycontainer
that can store one element of any type and that it has just one member
function called
increase, which increases its value. But we
find that when it stores an element of type
char it would be
more convenient to have a completely different implementation with a
function member
uppercase, so we decide to declare a class
template specialization for that type:
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// template specialization
#include <iostream>
using namespace std;
// class template:
template <class T>
class mycontainer {
T element;
public:
mycontainer (T arg) {element=arg;}
T increase () {return ++element;}
};
// class template specialization:
template <>
class mycontainer <char> {
char element;
public:
mycontainer (char arg) {element=arg;}
char uppercase ()
{
if ((element>='a')&&(element<='z'))
element+='A'-'a';
return element;
}
};
int main () {
mycontainer<int> myint (7);
mycontainer<char> mychar ('j');
cout << myint.increase() << endl;
cout << mychar.uppercase() << endl;
return 0;
}
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J
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This is the syntax used in the class template specialization:
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template <> class mycontainer <char> { ... };
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First of all, notice that we precede the class template name with an
empty
template<> parameter list. This is to explicitly
declare it as a template specialization.
But more important than this prefix, is the
<char>
specialization parameter after the class template name. This
specialization parameter itself identifies the type for which we are
going to declare a template class specialization (
char). Notice
the differences between the generic class template and the
specialization:
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2
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template <class T> class mycontainer { ... };
template <> class mycontainer <char> { ... };
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The first line is the generic template, and the second one is the
specialization.
When we declare specializations for a template class, we must also
define all its members, even those exactly equal to the generic template
class, because there is no "inheritance" of members from the generic
template to the specialization.
from:
http://www.cplusplus.com/doc/tutorial/templates/
posted on 2010-05-03 22:11
chatler 閱讀(470)
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