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hugmynutus 21 hours ago

> I don't see what should ever be wrong with a function pointer. [...]Care to explain what's the issue here?

1. You're writing code you don't have to

2. That adds runtime overhead

3. That when you screw up has non-trivial security & resource management side effects

This is objectively indefeasible in nearly any vaguely professional context.

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jstimpfle 20 hours ago | parent [-]

1. No, you're not writing code you don't have to. It's not different to implementing this as non-virtual methods, in fact I'd argue doing simple functions is more straightforward.

2. And the code being compiled is abstract & generic, it won't be instantiated for every type and bloat the executable or instruction cache.

3. Security concerns: With C++ virtual methods every object carries a mutable pointer too (to a vtable containing function pointers). What resource management side effects please?

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kllrnohj 14 hours ago | parent [-]

Re #3: vtable pointers aren't mutable...?

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jstimpfle 10 hours ago | parent [-]

Of course they are. The pointers to the vtable are part of the object. They aren't mutable fields as per the language, but for security concerns it doesn't matter what the language thinks. Being part of the object, the vtable pointer has to live in a writeable memory mapping (like stack / heap).

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Conscat 7 hours ago | parent | next [-]

Clang pointer authentication makes any type of vtable attack impossible in C++.

	▲	jstimpfle 7 hours ago \| parent [-]
		Fair enough, this is an extension though and I suppose you could use it with manually constructed vtables as well?

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kllrnohj 6 hours ago | parent | prev [-]

Then I don't understand your argument. If you're just saying what could go wrong with heap corruption, then your vtable complaint also applies to storing function pointers in arena allocators in Zig? Zig doesn't have anything special here?

	▲	jstimpfle 2 hours ago \| parent [-]
		I asked you what's wrong with pool destructor function pointers. You gave a reason what's wrong and I refuted it. So no, I'm not saying that storing a function pointer is special, just that nothing's wrong with it. (And implying that since there's nothing wrong and it's probably the most straightforward thing to do, it's also probably the right thing).