On Friday, 4 September 2015 at 19:25:35 UTC, H. S. Teoh wrote:
Wait, wait, did I miss something? Since when was operator
overloading allowed as free functions? Or is opEquals a special
case?
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:
http://dlang.org/operatoroverloading.html#equals
but TDPL also talks about it. But as part of the fix for
https://issues.dlang.org/show_bug.cgi?id=9769
we need to templatize the free function opEquals so that it
doesn't require Object. Then opEquals on a class will take
whatever the most base class in your class hierarchy is that has
opEquals rather than Object, and we can actually deprecate
opEquals on Object (though that may require some additional
compiler help rather than simply deprecating it; I'm not sure).
Regardless, templatizing the free function version of opEquals is
the first step towards that.
- Jonathan M Davis
