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Date: Sat, 23 Jan 2016 21:02:18 +0000
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Subject: Re: [RFC] Generalize support of negative string offsets
From: ajf@ajf.me (Andrea Faulds)

Hi François,

François Laupretre wrote:

> Starting discussion about https://wiki.php.net/rfc/negative-string-offsets
>
> Please read and comment.

I like this RFC. Being able to use negative offsets helps code 
readability, but it not being universally supported is annoying. I like 
that this brings more consistency.

I particularly like that this is supported for string indexing with the 
[]/{} operator.

At present a negative offset is interpreted as being the maximum string 
length plus that offset, so $str[-1] is equivalent to $str[(2**64 - 1) - 
1]. In practice, this means you will get an empty string and an 
"Uninitialized string offset:" E_NOTICE. It's not useful except for 
extremely large strings and so I suspect that behaviour comes from an 
implementation detail (naïve signed-to-unsigned integer conversion).

What you're proposing is to have the negative offset be interpreted as 
an offset from the end of the string, as the built-in functions do. This 
is more useful, but it's a change of behaviour from the present one, and 
thus a backwards-compatibility break, even if it's unlikely to affect 
real-world code. So, you might wish to mention that.

Also, I think the RFC would be more accessible if you included some 
examples of where to use negative offsets. That would give readers an 
at-a-glance view of what the RFC changes.

Anyway, I like what you're doing here. Thanks for the proposal!

-- 
Andrea Faulds
https://ajf.me/