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Date: Thu, 22 Mar 2007 15:54:36 +0100
To: "Christian Schneider" <cschneid@cschneid.com>
Cc: internals@lists.php.net
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Subject: Re: [PHP-DEV] PATCH: anonymous functions in PHP
From: michael.walter@gmail.com ("Michael Walter")

On 3/22/07, Christian Schneider <cschneid@cschneid.com> wrote:
> Michael Walter wrote:
> > Which seems to fit Andi's $_SCOPE proposal.
>
> Yes, but is a point against a real closure proposal.

I think the defining property of a "real" closure proposal is having
the lexical scope available.
So I guess we both agree on that something like $_SCOPE would be a
useful thing to have.

> >> He said real-life examples (-:C
> >
> > Is that like "enterprise" examples? ;)
>
> No, it's like non-textbook example (which can also run on a Bird of Prey
> or a Klingon starship :-))

Closures become really useful when you start building abstractions on
top of anonymous functions, since in the process of abstraction you
often replace literals/constants by parameters (similar to how
function parameters become useful when you start refactoring common
code into functions ;).

A simple real-life example is:

function pick($member)
{
  return create_function('$x', 'return $x->'.$member.';');
}

which could be used e.g. in

  array_map(pick('age'), $people).

Arguably, in this case you could as well write:

  array_map(function($p) {return $p->age;}, $people);

but I believe it is easy to see how the problem generalizes.

Regards,
Michael