Thanks for help,
I have an additional question. Does anyone know why the following
program gives different output on VC++ 6 and VC++ 2003 NET? It is pretty
strange, isn't it?
Thanks in advance.
Pshemek
#include <iostream>
#include <cmath>
using namespace std;
class A
{
protected:
char m_d;
};
class B : public A
{
public:
typedef char s;
private:
unsigned short g;
};
class C : public A
{
public:
typedef short unsigned s;
private:
unsigned d;
};
template<bool cond>
class Select {};
template<> class Select<true>
{
static void Statment1(double g)
{
cout << g*g << endl;
}
public:
static void f(double g)
{
Statment1(g);
}
};
template<> class Select<false>
{
static void Statment2(double g)
{
cout << sqrt(g) << endl;
}
public:
static void f(double g)
{
Statment2(g);
}
};
template<bool cond> void exec()
{
Select<cond>::f(3.0);
}
template<class T>
void foo()
{
exec();
exec();
}
int main()
{
foo<B>();
foo<C>();
return 0;
}
-----Original Message-----
From: boost-users-bounces@lists.boost.org
[mailto:boost-users-bounces@lists.boost.org] On Behalf Of Eric Niebler
Sent: 11 May 2005 18:37
To: boost-users@lists.boost.org
Subject: [Boost-users] Re: Question
Sliwa, Przemyslaw (London) wrote:
I would like to write a template which depending on the argument type
does different things.
For example the pseudo code:
template
foo(T& nT, C& nC)
{
// common code;
if(T==C)
// specific code;
.....
// again common code;
}
Can the template meta programming help me in this case?
It may. It depends on whether "specific code" compiles when T!=C. If it
does, you could do this:
template
void foo(T& nT, C& nC)
{
// common code
if(boost::is_same::value)
{ /* specific code */ }
// again common code
}
where is is_same<> is defined in boost/type_traits/is_same.hpp. If
"specific code" doesn't compile when T!=C, you need to get fancier. An
overloaded helper function is the way to go:
template
void specific_code(T&, C&) {}
template<class T>
void specific_code(T&, T&)
{
// specific code here
}
template
void foo(T& nT, C& nC)
{
// common code
specific_code(nT, nC);
// again common code
}
HTH,
--
Eric Niebler
Boost Consulting
www.boost-consulting.com
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