Frustrations with const

[H. S. Teoh]

I'm writing an AA implementation, and ran into this problem with the way
const behaves in D. Basically, I have an auxiliary function that
searches the internal hash table for a given key, and returns the slot
containing the matching entry, if found.

The problem is, how to write this function so that it can be called from
*both* a const public method and a non-const public method? Since the
method itself doesn't actually modify anything, it *should* in theory be
possible to mark it as const:

	const Slot *findSlot(Key key) { ... }

However, because the const applies to 'this', the compiler insists that
referencing anything via 'this', including reading a pointer to a slot,
must also be const, so it refuses to let the return type be Slot*; it
has to be const(Slot)*.

But this is silly, because now the caller isn't allowed to modify the
Slot either, so now I need to bloat the code with two identical copies
of findSlot, one with const, and one without (since if it wasn't marked
const, then a const method couldn't call it).

Is there any way to work around this?

Or more importantly, why does the compiler force all internal members of
this to be const inside a const method, when what it really should be
enforcing is that nothing is being *modified*? What's wrong with
extracting non-const members from the object in a const method, if you
never actually do anything to it?


T

-- 
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