On Sunday, 15 May 2022 at 15:26:40 UTC, Kevin Bailey wrote:
I've done some scripting in D over the years but I never dug
into D until recently. I'm going through Learning D and I was
reminded that structs and classes are so different.
- struct methods are non-virtual while class methods are virtual
- Thus, structs can't inherit, because how would you find the
child's destructor given a parent pointer?
- On the stack, structs by-value but classes are by-reference
I'm trying to understand why it is this way. I assume that
there's some benefit for designing it this way. I'm hoping that
it's not simply accidental, historical or easier for the
compiler writer.
A virtual function call has to pass through a virtual function
look-up, and thus there is (some) overhead involved.
Thus, by design, structs avoid this overhead (completely).
It's also (I think) another reason why D does not support
multiple inheritance. Since you would need multiple virtual
function tables.
