Get class size of object

[Simen Kjaeraas]

On 2013-08-11, 20:33, JS wrote:

> I think you're missing the point to some degree(I realize there is a  
> diff between an object and a type, but I should be able to easily get  
> the class size of an object at run time regardless if the object is  
> typed as a base class). The code below does this, but at a cost of  
> verbosity.
>
> Here is code that exactly demonstrates what I am essentially trying to  
> do. The only drawback now is having to mixin the template for each class  
> which I would want to automate and it would be nice to wrap the RT and  
> CT methods in subclasses without overhead.

It would appear that some information is lost when calling typeid from an
interface. I would have expected this to work:

interface I {
     final
     size_t size() {
         return typeid(this).init.length;
     }
}

class A {}

class B : A, I {
     int a;
}

void test1() {
     I i = new B();
     assert(i.size > 0); // Fails.
}


A bit more experimentation shows:

void test2() {
     B b = new B();
     I i = b;
     A a = b;

     assert(typeid(a) == typeid(b)); // Passes.
     assert(typeid(i) == typeid(b)); // Fails.

     assert(typeid(b).init.length > 0); // Passes.
     assert(typeid(i).init.length > 0); // Fails.
}


It appears thus that the error is in typeid(interface), which does not
give the actual typeid.

The workaround is as follows:


interface I {
     final
     size_t size() {
         return typeid(cast(Object)this).init.length;
     }
}


Is this what you want? Is it good enough? I have no idea, as you're
notoriously bad at describing what you want, but pretty good at
attacking people.

If you're looking for a no-overhead solution, then this might not be
good enough. I'm surprised that a virtual function call is fine,
though.