带有模板类的c ++中的多态性

Question

I would like to use a templated class in c++ with one of the template argument determined by user input in run-time. I am pretty sure there is an easy and nice way to do it but I am quite new to c++ and I am still struggling with polymorphism and template classes...

Here is what I would like to do:

if (argument==0)
      typedef Class1 ActualClassUsed;
if (argument==1)
      typedef Class2 ActualClassUsed;

MyTemplatedClass<ActualClassUsed> * object= MyTemplatedClass<ActualClassUsed>::New();

obviously in the example above ActualClassUsed is not defined in the proper scope... Any easy way to correct this ?

Thanks for your help !

Answer 1

Templates is actually duplicating the same code with corresponding data( needed data types only ,not all ) types.That is actually happens at compile time.

Templates is useful when different data type's (either user defined or built in data types) process in the same way

currently it is not possible to instantiate template at run-time.

Answer 2

I would like to use a templated class in c++ with one of the template argument determined by user input in run-time. I am pretty sure there is an easy and nice way to do it

Nope there isn't. It's actually fundamentally impossible by design.

Templates are a developer tool which generates code the moment you compile your program, which hopefully happens before it is run by any user, time travel aside it is pretty hard to use an information before someone gave it to you.

You can't decide on a fixed color for the car you're building in your factory based on which day the futur driver is going to use it. If you want something like that it has to be a dynamic chameleon like color which changes based on the day.