On Saturday, 5 September 2015 at 09:45:36 UTC, Jacob Carlborg
wrote:
On 2015-09-05 08:26, Jonathan M Davis wrote:
Clearly, you haven't read TDPL recently enough. ;)
There is a free function, opEquals, in object.d which gets
called for
classes, and _it_ is what == gets translated to for classes,
and it
calls the member function version of opEquals on classes:
https://github.com/D-Programming-Language/druntime/blob/master/src/object.d#L143
This allows us to avoid a number of fun bugs with opEquals
that you get
in languages like Java and makes it completely unnecessary to
do stuff
like check whether the argument to opEquals is null. Timon
gave the link
to the explanation in the spec:
Bu you don't see my example as a problem?
Well, it might be a bit annoying, but it's simply a matter of
adjusting your code to call opEquals explicitly when trying to
call the base version, whereas without the free function
opEquals, you have subtle correctness problems. For instance, if
you have base == derived and derived == base, you'll get the same
result for both for D, whereas the equivalent Java or C# could
would likely not, because the free function opEquals checks both
lhs.opEquals(rhs) and rhs.OpEquals(lhs) whether you did base ==
derived or derived == base.
So, while what we have is by no means perfect, I think that it is
an improvement over what Java and C# did.
- Jonathan M Davis
