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Date: Wed, 02 Jun 2021 18:47:29 -0500
To: "php internals" <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Regarding array_shift()/array_unshift()
From: larry@garfieldtech.com ("Larry Garfield")

On Wed, Jun 2, 2021, at 6:15 PM, Mike Schinkel wrote:
> > On Jun 2, 2021, at 7:07 PM, Larry Garfield <larry@garfieldtech.com> wrote:
> > 
> > On Wed, Jun 2, 2021, at 5:59 PM, Mike Schinkel wrote:
> >>> On Jun 2, 2021, at 4:25 AM, Jordi Boggiano <j.boggiano@seld.be> wrote:
> > 
> >>> IMO for unshift() it'd be fine to return a new array, but when processing a list of things in a FIFO pattern I often used array_shift() to get the first "job" out of the array. If $array->shift() returns a new array then how do I access the first item?
> >> 
> >> That is a really excellent point, something I did not think to consider 
> >> given how rarely I use array_shift().  
> >> 
> >> But your comment causes me to ponder a number of follow up questions, 
> >> some of which are tangential.  If any reader feels these tangents are 
> >> worth discussing please make another email and quote my relevant 
> >> comments so we can have a dedicated thread for each.
> >> 
> >> 1.) Given Nikita's position that it would only be viable to offer a 
> >> syntax that simulates method calling for arrays if the methods 
> >> themselves are immutable can you envision a solution for allowing  
> >> $array->shift() functionality that would address getting both element 
> >> and shifted array without resorting to by-reference parameters?
> > 
> > $list->head() (returns first item)
> > $list->tail() (returns all items but the first one)
> 
> I assume $list->tail() would still have the O(<n>) problem in PHP, though?
> 
> -Mike

If implemented like an array, yes.  If implemented in a more efficient way in C, potentially not.  Or at least a smaller constant multiplier with n.  (If something is O(n) but the cost per in is very small, then it being O(n) is not a big deal.  If the cost per n is huge, it's a very huge deal.)

--Larry Garfield