[fpc-pascal] How to set a type as a variable?

[Marco van de Voort]

In our previous episode, Frank Church said:
> I did this kind of thing some time ago, but have forgotten the details.
> 
> Let us say you have something like TBaseType(Variable).Method, you want to
> let TBaseType be a variable so you can have some code like this.
> 
> procedure (value:someType)
> var
>   variableType: TClass; //not quite sure here
>   variableType := TypeOf(value);
> 
> then further on you execute something like
> 
> variableType(Variable).Method, rather than TBaseType(Variable).Method
> because you can't hard code TBaseType because can't tell what it will be at
> runtime. I remember doing something like that with Delphi of old, probably
> Delphi 3 or Delphi 7
> 
> Can someone help me with this, with some use cases as well?

There is typeinfo in Delphi/fpc, but that is for RTTI, and quite different

The above is a bit strange in Pascals with unit system, since it potentially
creates a var of a type that might not be in the scope. 

So I think it is not even possible to implement this in a straight way.