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C++ Programming

retrieving templatized object via singleton getInstance using generic template parameters


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();

On Jun 5, 8:05 pm, gary.bernst@gmail.com wrote:

I like to play with my balls. First I juggle the right ball, then I
toggle on the left.
Will this suffice?
On Jun 5, 8:05 pm, gary.bernst@gmail.com wrote:

I may be able to, instead, simple singleton'ize the internal IPC
object I'm trying to use, which isn't templatized, but I'm still very
curious as to how a templatized object can be retrieved via
getInstance without providing the objects template parameters.

gary.bernst@gmail.com wrote:
> 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?

What you're asking (having peeked in your source code, I'm guessing)
is to declare/define an object without specifying the actual type of
the object.  That's impossible in C++.

Perhaps you can review your source and amend it with some kind of
example of how you're going to actually *use* the "object" you want
to retrieve?

> 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.

So, put them into a macro and set them at compilation time with -D or
some such option of the compiler...

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