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.
One problem that this causes is that I have to remember different
rules when using them. This creates the additional load of
learning and remembering which types are which from someone
else's library.
A bigger problem is that, if I have a struct that I suddenly want
to inherit from, I have to change all my code. In addition to
that work, in both of these cases, one could easily do it wrong:
// Fine with a struct, fatal with a class.
Foo foo;
At least in C++, the compiler would complain. In D, not even a
warning.
Why is it this way? What is the harm of putting a class object on
the stack?
