[boost] intrusive tagging allows omision of unneeded headers

From: Thorsten Ottosen (nesotto_at_[hidden])
Date: 2003-01-08 08:42:58

Hi boosters,

just want to show you something I discovered
(maybe you already know) which allows template functions to be specialized
for a class without including its header; it does require that classes are
changed internally,
but I assume it will make compilation mucho faster. (another problem is that
I can only
compile it with Comeau, neither GCC 3.2 or vc7 can eat it).

Anyway, the example is quite straightforward:

#include <iostream>

using namespace std;

template< typename C >
void foo( const C& c )
{
    foo_impl( c, C::tag() );
}

template< typename C, typename Tag >
void foo_impl( const C& c, Tag t )
{
    cout << "default version" << endl;
}

template< typename C >
void foo_impl( const C& c, typename C::bar_tag )
{
    cout << "bar specialised version" << endl;
}

class X
{
public:
    class tag {};
    typedef tag X_tag;
};

class bar
{
public:
    class tag {};
    typedef tag bar_tag;
};

int main()
{
    X x;
    bar b;

    foo( x );
    foo( b );

    return 0;
}

Maybe somebody can use it to something in the future?

regards

Thorsten Ottosen, Aalborg University
nesotto_at_[hidden]
---------------------------------------------------
C++:

my_map[key]++;

Java:

if ( !my_map.containsKey( key ) )
    my_map.put( key, new Integer( 1 ) );
else
{
    Integer count = ( Integer )my_map.get( key ) );
    int icount = count.IntValue();
    my_map.put( key, new Integer( ++icount ) );
}