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Date: Sun, 8 Aug 2021 17:52:02 +0100
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Subject: Re: [PHP-DEV] Revisiting Userland Operator Overloads
From: rowan.collins@gmail.com (Rowan Tommins)

On 08/08/2021 16:39, Larry Garfield wrote:
> 1) Implementing an interface and stubbing out some methods is a lie. It's a lie the engine won't stop you from telling, but it's still a lie.  If you only support addition and division, for instance (add to a collection and split a collection into several), then having a bunch of comparison methods that your object says you support but the program dies as soon as you use it is a lie, and a landmine waiting to happen.


I find it odd, given your other comments, that you keep coming back to 
collection examples, which seem to me very much in the realm of 
re-defining the symbols to mean something different in a new domain. If 
"+" can mean "union" and "/" mean "partition", why not also let "<<" 
mean "append"?

If we're saying we don't want "arbitrary weirdness", then discouraging 
"add" and "divide" on a collection feels like a feature, not a bug.


> 2) As Jordan demonstrated, there are many even formally defined situations where some of the operators are explicitly meaningless.


Yes, and as I demonstrated, there are situations where some of the 
operators are only meaningful for a subset of operands. Saying that a 
Money object is "Multipliable" would also be "a lie", since multiplying 
two Money objects together is a logic error, even though multiplying 
Money by a unit-less number is very useful.


Regards,

-- 
Rowan Tommins
[IMSoP]