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0 pointswosined6mo ago0 comments

> If there is no polymorphism, you don't use a vtable at all, that's saving even more space.

Not true. You use a vtable even if there is no polymorphism, in cases where you want to have objects store pointers to their methods (OO interface), but don't want each instance to have pointers to all methods. I was referring to this article, which the OP links in his post https://lwn.net/Articles/444910/

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17186274406mo ago

When do objects need to have function pointers? If the function never changes per object, then you would just directly call the function. When do you use function pointers? When the caller only knows the type of struct foo_ops, but not the actual called function. That's polymorphism.

wosinedOP6mo ago

> When do objects need to have function pointers?

You can redefine the methods at runtime. If for example I have a logger that logs on the local drive and another one that logs on a networked drive I can swap the method pointer. This is not polymorphism since the object does have to change. I can also load the function from a shared library that is unknown during compilation and use that as part of the objects methods.

17186274406mo ago

I would call that polymorphism, since the object type the caller sees, still stays the same, i.e. the vtable itself or some containing struct/class. So as far as the caller is concerned, the object he has access to behaves differently.

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0 pointswosined6mo ago0 comments

> If there is no polymorphism, you don't use a vtable at all, that's saving even more space.

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17186274406mo ago

wosinedOP6mo ago

> When do objects need to have function pointers?

17186274406mo ago

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