kmail/pluginloader.h

/*  -*- c++ -*-
    This file is part of libkdepim.

    Copyright (c) 2002,2004 Marc Mutz <mutz@kde.org>

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
    License as published by the Free Software Foundation; either
    version 2 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Library General Public License for more details.

    You should have received a copy of the GNU Library General Public License
    along with this library; see the file COPYING.LIB.  If not, write to
    the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
    Boston, MA 02111-1307, USA.
*/

#ifndef __KPIM_SHARED_PLUGINLOADER_H__
#define __KPIM_SHARED_PLUGINLOADER_H__

#include <pluginloaderbase.h>

namespace KPIM {

  /**
   * @short A generic plugin loader for when KPart::Plugin is overkill
   * @author Marc Mutz <mutz@kde.org> based on KABC's FormatFactory
   *
   * This is a generic plugin loader / factory for small plugins that
   * don't want to be QObjects.
   *
   * @sect Usage
   *
   * A PluginLoader takes two template arguments, <code>T</code> and
   * <code>T_config</code>:
   *
   * <dl>
   * <dt>T</dt><dd>The type of object to return</dd>
   * <dt>T_config::mainfunc</dt><dd>The suffix of the factory function to call
   *          in the library to obtain a new object of type <code>T</code>.
   *          The string passed to <code>KLibrary::symbol()</code> is
   *          <code>libName_mainfunc</code>.</dd>
   * <dt>T_config::path</dt><dd>The search pattern for <tt>.desktop</tt> files
   *          containing the plugin descriptions. This is the string passed as
   *          the @p filter argument to
   *          <code>KStandardDirs::findAllResources</code>.</dd>
   * </dl>
   *
   * The last two parameters being strings, they are passed via an
   * encapsulating class, of which <code>mainfunc</code> and
   * <code>path</path> are public static members:
   *
   * <pre>
   * struct MyObjectPluginLoaderConfig {
   *   static const char * const mainfunc;
   *   static const char * const path;
   * };
   * const char * const MyObjectPluginLoaderConfig::mainfunc = "myapp_create_myobject";
   * const char * const MyObjectPluginLoaderConfig::path = "myapp/plugins/ *.desktop";
   * </pre>
   *
   * You would then use a <tt>typedef</tt> to create a less unwieldy
   * name for your plugin loader:
   *
   * <pre>
   * typedef KPIM::PluginLoader< MyObject, MyObjectPluginLoaderConfig > MyObjectPluginLoader;
   * </pre>
   *
   * All of this is what the
   * <code>KPIM_DEFINE_PLUGIN_LOADER(pluginloadername,type,mainfunc,path)</code> macro
   * achieves.
   *
   **/
  template< typename T, typename T_config >
  class PluginLoader : public PluginLoaderBase {
  protected:
    PluginLoader() : PluginLoaderBase() {}

  private:
    static PluginLoader<T,T_config> * mSelf;

  public:
    virtual ~PluginLoader() { mSelf = 0; }

    /** Returns the single instance of this loader. */
    static PluginLoader<T,T_config> * instance() {
      if ( !mSelf ) {
	mSelf = new PluginLoader<T,T_config>();
	mSelf->scan();
      }
      return mSelf;
    }

    /** Rescans the plugin directory to find any newly installed
	plugins.
    **/
    virtual void scan() {
      doScan( T_config::path );
    }

    /** Returns a pointer to a plugin object (of type @p T) or a null
        pointer if the type wasn't found. You can extend this method
        for when you want to handle builtin types */
    virtual T * createForName( const QString & type ) const {
      void * main_func = mainFunc( type, T_config::mainfunc );
      if ( !main_func ) return 0;

      // cast to a pointer to a function returning T*, call it and
      // return the result; don't you love C? ;-)
      return ((T* (*)())( main_func ))();
    }
  };

  template< typename T, typename T_config >
  PluginLoader<T,T_config> * PluginLoader<T,T_config>::mSelf = 0;

};

#define KPIM_DEFINE_PLUGIN_LOADER( pl, t, mf, p ) \
  namespace { /* don't pollute namespaces */ \
    struct pl##Config { \
      static const char * const mainfunc; \
      static const char * const path; \
    }; \
    const char * const pl##Config::mainfunc = mf; \
    const char * const pl##Config::path = p; \
  }; \
  typedef KPIM::PluginLoader< t, pl##Config > pl; \
      

#endif // __KPIM_SHARED_PLUGINLOADER_H__