include/wvmoniker.h

   1 /* -*- Mode: C++ -*-
   2  * Worldvisions Weaver Software:
   3  *   Copyright (C) 1997-2002 Net Integration Technologies, Inc.
   4  *
   5  * Support for monikers, which are strings that you can pass to a magic
   6  * factory to get objects supporting a particular interface, without actually
   7  * knowing anything about the constructor for those objects.
   8  */
   9 #ifndef __WVMONIKER_H
  10 #define __WVMONIKER_H
  11
  12 #include "wvstring.h"
  13 #include "wvxplc.h"
  14
  15 class WvMonikerRegistry;
  16
  17 typedef void *WvMonikerCreateFunc(WvStringParm parms, IObject *obj);
  18
  19 /**
  20  * WvMonikerBase is an auto-registration class for putting things into
  21  * a WvMonikerRegistry.  When a WvMonikerBase instance is created, it
  22  * registers a moniker prefix ("test:", "ssl:", "ini:", etc) and a factory
  23  * function that can be used to create an IObject using that prefix.
  24  *
  25  * When the instance is destroyed, it auto-unregisters the moniker prefix
  26  * from the registry.
  27  *
  28  * You can't actually create one of these, because it's not typesafe.  See
  29  * WvMoniker<T> instead.
  30  */
  31 class WvMonikerBase
  32 {
  33 protected:
  34     WvMonikerBase(const UUID &iid, WvStringParm _id,
  35                   WvMonikerCreateFunc *func, const bool override = false);
  36     ~WvMonikerBase();
  37
  38 public:
  39     WvString id;
  40     WvMonikerRegistry *reg;
  41 };
  42
  43
  44 /**
  45  * A type-safe version of WvMonikerBase that lets you provide create functions
  46  * for object types other than IObject.  (The objects themselves have to
  47  * be derived from IObject, however.)
  48  *
  49  * See WvMonikerBase for details.
  50  *
  51  * Example:
  52  *    static IWvStream *createfunc(WvStringParm s, IObject *obj,
  53  *                                 void *userdata)
  54  *    {
  55  *        return new WvStream;
  56  *    }
  57  *
  58  *    static WvMoniker<IWvStream> registration("ssl", createfunc);
  59  */
  60 template <class T>
  61 class WvMoniker : public WvMonikerBase
  62 {
  63 public:
  64     typedef T *CreateFunc(WvStringParm parms, IObject *obj);
  65
  66     WvMoniker(WvStringParm _id, CreateFunc *_func, const bool override = false)
  67         : WvMonikerBase(XPLC_IID<T>::get(), _id, (WvMonikerCreateFunc *)_func,
  68                         override)
  69     {
  70         // this looks pointless, but it ensures that T* can be safely,
  71         // automatically downcast to IObject*.  That means T is really derived
  72         // from IObject, which is very important. The 'for' avoids a
  73         // warning.
  74         for(IObject *silly = (T *)NULL; silly; )
  75             ;
  76     };
  77 };
  78
  79
  80 /**
  81  * Create an object registered in a WvMonikerRegistry.  The iid specifies
  82  * which registry to look in, and s, obj, and userdata are the parameters to
  83  * supply to the object's factory.  Most factories need only 's', which is the
  84  * moniker itself.
  85  *
  86  * Most people don't use this function.  See the templated, type-safe version
  87  * of wvcreate() below.
  88  */
  89 void *wvcreate(const UUID &iid, WvStringParm s, IObject *obj);
  90
  91
  92 /**
  93  * Create an object registered in a WvMonikerRegistry.  Exactly which
  94  * registry is determined by the template type T.
  95  *
  96  * s, obj, and userdata are the parameters to supply to the object's
  97  * factory.  Most factories need only 's', which is the moniker itself.
  98  *
  99  * Example:
 100  *    IWvStream *s = wvcreate<IWvStream>("tcp:localhost:25");
 101  *    IWvStream *s_ssl = wvcreate<IWvStream>("ssl:", s);
 102  */
 103 template <class T>
 104 inline T *wvcreate(WvStringParm s, IObject *obj = 0)
 105 {
 106     return (T *)(wvcreate(XPLC_IID<T>::get(), s, obj));
 107 }
 108
 109
 110 #endif // __WVMONIKER_H