gcc 4.7.3 不支持成员函数模板特化。如下代码：
#ifndef __MEMFUNTEMPLATE_H__
#define __MEMFUNTEMPLATE_H__
#include <stdio.h>
class Base {};
class Derived : public Base {};
struct Functor {
template <typename T> void function() {
printf(" Primary template
.\n");
}
template<>
void function< int >(){
printf(" Specialization for int.\n");
}
template<> void function<Base *>() {
printf(" Specialization for Base *.\n");
}
};
class Tester {
public :
static void DoTest()
{
Functor functor;
functor.function< char >();
functor.function< int >();
functor.function<Base *>();
functor.function<Derived *>();
}
};
#endif // __MEMFUNTEMPLATE_H__
#define __MEMFUNTEMPLATE_H__
#include <stdio.h>
class Base {};
class Derived : public Base {};
struct Functor {
template <typename T> void function() {
printf(" Primary template
.\n"); }
template<>
void function< int >(){
printf(" Specialization for int
.\n"); }
template<> void function<Base *>() {
printf(" Specialization for Base *
.\n"); }
};
class Tester {
public :
static void DoTest()
{
Functor functor;
functor.function< char >();
functor.function< int >();
functor.function<Base *>();
functor.function<Derived *>();
}
};
#endif // __MEMFUNTEMPLATE_H__
在 VS2010 中编译运行是没有问题的，但在 gcc 4.7.3下，编译都通不过：
../src/MemFunTemplate.h:21:14: error: <strong> explicit specialization in non- namespace scope</strong> ‘ struct Functor’
../src/MemFunTemplate.h:22:24: error: template-id ‘function< int>’ in declaration of primary template
../src/MemFunTemplate.h:26:14: error: explicit specialization in non- namespace scope ‘ struct Functor’
../src/MemFunTemplate.h:26:38: error: template-id ‘function<Base*>’ in declaration of primary template
../src/MemFunTemplate.h:26:21: error: ‘ void Functor::function()’ cannot be overloaded
../src/MemFunTemplate.h:22:10: error: with ‘ void Functor::function()’
../src/MemFunTemplate.cpp: In function ‘ int main()’:
../src/MemFunTemplate.cpp:17:2: error: ‘DoTest’ is not a member of ‘Functor’
为了达到近似成员函数模板特化的效果，可以利用成员函数主模板以及重载函数来实现：
/*
* MemFunTemplate.h
*
* Created on: Jul 12, 2013
*/
#ifndef MEMFUNTEMPLATE_H_
#define MEMFUNTEMPLATE_H_
#include <stdio.h>
template<typename T>
struct DummyIdentity {
typedef T type;
};
class Base {};
class Derived : public Base {};
struct Functor {
template <typename T> void function() {
function(DummyIdentity<T>());
}
private :
template <typename T>
void function(DummyIdentity<T>) {
printf(" Primary template DummyIdentity<T> .\n");
.\n"); }
void function(DummyIdentity<int>) {
printf(" overload function for DummyIdentity<int> .\n");
.\n"); }
void function(DummyIdentity<Base *>) {
printf(" overload function for DummyIdentity<Base *> .\n");
.\n"); }
};
class Tester {
public :
static void DoTest()
{
Functor functor;
functor.function<char>();
functor.function<int>();
functor.function<Base *>();
functor.function<Derived *>();
}
};
#endif /* MEMFUNTEMPLATE_H_ */
调用 DoTest() 运行结果如下：
Primary template DummyIdentity<T> .
. overload function for DummyIdentity< int> .
. overload function for DummyIdentity<Base *> .
. Primary template DummyIdentity<T> .
.
注意：
VS2010 版本的代码，模板形参为 T，在实例化不会进行隐式类型转换。即用 Derived * 当作实参调用的是主模板，而不是 Base * 特化版本
而在 gcc 下，模板形参虽然也为T，但影响重载决议的 function 参数为：DummyIdentity<T>，用不同的实际参数实例化该模板，得到的是一堆重载函数。因此用 Derived * 当作实参时，调用的函数自然就是实例化的 void function(DummyIdentity<T>)了。
