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Date: Thu, 21 Jul 2016 12:51:38 -0300
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To: PHP Internals <internals@lists.php.net>
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Subject: RFC: lazy statements
From: david.proweb@gmail.com (David Rodrigues)

This Feature Request is about the implementation of lazy statements.

Basically it should implements a 'lazy' keyword (or similar) and
structured like an anonymous function, except that it doesn't accepts
arguments, but accept the use() feature.

    $var = lazy { return 1; }
    $var = lazy use ($x) { return $x; }

It differ from anonymous function because this assignment is treated
as variable, without need to call or check if it is a valid Closure
all the time.

---

Execution example:

    echo $var;
    echo $var;

In this example, the first echo will execute the lazy statement and
set the returned value directly to $var container, then will echo 1.
The second echo will not execute the lazy anymore, because it was
processed on first echo, so will just echo 1.

---

It should be very useful on framework or package development because
you can defines lazy properties that need to be calculated only when
it is requested the first time.
Should be useful too when you have a global variable like $user that
you should not use all the time (in all requests).

    View::share('user', lazy { return User::find(session('user.id')); });

This code will be executed only on try read or write on $user variable.

---

It should works from read or write, to the next code is valid:

    $var = lazy { return [ 1, 2, 3 ]; };
    $var[] = 4;

---

Currently it is possible do it in a very hackish way: by using magic
getter, by create a user getter or a own implementation of this
feature.
All this ways have a lot of limitations.

A hackish example that shows how it should works on current PHP
version: http://pastebin.com/cz93wL7n

---

I tell more about that here: https://bugs.php.net/bug.php?id=72637

-- 
David Rodrigues