On 17/09/2024 21:37, Rob Landers wrote:
I would prefer to see something simple, and easy to reason about. We
can abuse some mathematical properties to result in something quite
simple:
1. If both are scalar, use existing logic.
2. If one is scalar and the other is not, use existing logic.
3. If one is scalar and the other overrides the operation, rearrange
the operation per its communitive rules so the object is on the
left. $scalar + $obj == $obj + $scalar; $scalar - $obj == -$obj +
$scalar, -($obj - $scalar). It is generally accepted (IIRC) that
when scalars are involved, we don’t need to be concerned with
non-abelion groups.
4. If both are objects, use the one on the left.
Step 3 requires operators to be overloaded in groups: the rearrangement
of the binary "-" operator requires definitions of both the unary "-"
operator and the binary "+" operator; and definitions that meet the
appropriate mathematical rules.
IMO, that's a lot more complicated than calling the "+" overload with an
OperandPosition::RightSide flag; or Python's approach of separate "add"
and "reflected add" magic methods.
Since you mentioned Scala, I looked it up, and it seems to be on the
other end of the spectrum: operators are just methods, with no
mathematical meaning or special dispatch behaviour. In fact, "a plus b"
is just another way of writing "a.plus(b)", so "a + b" is just a way of
writing "a.+(b)"
Maybe it would be "useful enough" to just restrict to left-hand side:
1. If the left operand is an object which implements the specified
operator, call that implementation with the right operand as argument
2. Else, proceed as current PHP.
This is where gathering a good catalogue of use cases would come in
handy: which of them would be impossible, or annoyingly difficult, with
a more restrictive resolution method?
Regards,
--
Rowan Tommins
[IMSoP]
