retrieving templatized object via singleton getInstance using generic template parameters

From:
 gary.bernstein@gmail.com
Newsgroups:
comp.lang.c++
Date:
Wed, 06 Jun 2007 03:05:44 -0000
Message-ID:
<1181099144.385317.258200@p77g2000hsh.googlegroups.com>
I want to call a singleton getInstance function to retrieve a
templatized object without knowing what types were used to create the
singleton object in the first call to getInstance. How can I do this
non-intrusively -- I.e., without, for example, typedef'ing the types
in every compilation unit?

Background:

Our code base has assert macros that need to reboot the system after
notifying components via a single templatized Component object that
contains the IPC object. I made the macro call a reboot function, but
that function needs to access the IPC object. I want to singleton'ize
the Component object to provide access to the IPC object, but don't
want to hand-code the template parameters in each compilation unit for
each getInstance call.

Code:

// I want to call retrieve a templatized object via a call to
getInstance
// without supplying the objects template parameters.
// Is there any way to do this, perhaps using template meta-
programming (TMP) techniques?

#include <string>
#include <iostream>

using namespace std;

template <typename T1, typename T2>
class Component
{

   public:

      static Component<T1, T2> getInstance()
      {
         static Component<T1, T2> t;
         return t;
      }

};

int main()
{

   // after the initial call to getInstance, here

   Component<int, string> & r1 = Component<int,
string>::getInstance();

   // I then want to call getInstance to obtain the same Component
without specifying the template params.

   Component<something generic> & r2 = Component<something
generic>::getInstance();
}

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