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Date: Thu, 25 Jan 2018 21:54:26 +0000
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Subject: Re: [PHP-DEV][RFC][DISCUSSION] Collection Inspection
From: rowan.collins@gmail.com (Rowan Collins)

On 25/01/2018 20:19, Michael Morris wrote:
> He's getting the syntax from Java.

Actually, from C++, and possibly from somewhere before that; at this 
point, it's pretty widely adopted.


> The problem is that Java already has the policing
> mechanics present in the runtime to police insertions into the collection
> and guarantee they are of the correct type. PHP has no such mechanism in
> place and in previous discussion threads the primary maintainers have
> underscored that adding such is highly difficult.

That's only partially true. As Bishop Bettini pointed out, you can 
*almost* get there with features already in the language, because you 
can implement the magic ArrayAccess interface and intercept all 
assignments using the $foo[]=$val and $foo[$bar]=$val syntaxes.

The main problem, as usual, is references: you can't intercept "$ref =& 
$foo[$bar]; $ref=42;" - if you try, you get a somewhat cryptic notice 
that "Indirect modification of overloaded element of foo has no effect". 
Apart from that, this is a *lot* simpler as a problem than general type 
tracking, because we only care about those two specific operations, not 
everywhere that performs an assignment of any sort.

In that sense, a full implementation of generics is actually simpler: 
the only actual type checks would be on parameters and return types, 
where they're already supported, e.g. class Stack<T> { public function 
push(T $item) { ... } public function pop(): T { ... } }

Like I say, it might be perfectly reasonable to have both a collectionof 
operator and generics in the language, but I don't think it's 
unreasonable to think about where they overlap.

Regards,

-- 
Rowan Collins
[IMSoP]