Req #51460 [Opn->Asn]: yield syntax construct
| From: | nikic@php.net | Date: | Tue, 05 Jun 2012 22:32:45 +0000 |
| Subject: | Req #51460 [Opn->Asn]: yield syntax construct | ||
| References: | 1 | Groups: | php.bugs |
| Request: | Send a blank email to php-bugs+get-171052@lists.php.net to get a copy of this message | ||
Edit report at https://bugs.php.net/bug.php?id=51460&edit=1
ID: 51460
Updated by: nikic@php.net
Reported by: a at b dot c dot de
Summary: yield syntax construct
-Status: Open
+Status: Assigned
Type: Feature/Change Request
Package: *Programming Data Structures
Operating System: Irrelevant
PHP Version: 5.3.2
-Assigned To:
+Assigned To: nikic
Block user comment: N
Private report: N
Previous Comments:
------------------------------------------------------------------------
[2010-04-02 01:37:18] a at b dot c dot de
Description:
------------
I draw your attention to the "yield" construct as used in Python, (recent) JavaScript, and
C#. This would be I think a nice way of creating Iterators for traversing complex objects.
A method that uses "yield" can be replaced by one that declares an instance of a custom
implementation of Iterator that takes $this and the method's arguments in its constructor, and
cranks through a state machine on each call of next(). (Microsoft's C# compiler handles it in
essentially this way, but has a much harder time of it because of things like multithreading and
explicit resource disposal.)
To some extent this can be done by hand now (I've done some work on a preprocessing script that
automates this) but in the absence of inner classes (which is what this Iterator ought to be) -
hint, hint - it plays havoc with visibility attributes.
Expected result:
----------------
/*
Example method that produces an inorder traversal of a binary tree.
foreach($btree->traverse_inorder() as $node)
{
do_something_with($node);
}
*/
public function traverse_inorder()
{
foreach($this->left->traverse_inorder() as $child)
{
yield $child;
}
yield $this;
foreach($this->right->traverse_inorder() as $child)
{
yield $child;
}
}
Actual result:
--------------
/*
The state machine that implements the body of the test script's function (identifies if the end
of the traversal has been reached, and obtains the next value to return if not)
*/
do
{
switch($this->_state)
{
case -1:
return false;
case 0:
// the object being traversed needs "left" made public
$this->_t1 = $this->_this->left->traverse_inorder();
reset($this->_t1);
$this->_state = 1;
case 1:
if(!($e = each($this->_t1)))
{
$this->_t1 = null;
$this->_state = 2;
continue;
}
$this->_value = $e['value'];
return true;
case 2:
$this->_value = $this->_this;
$this->_state = 3;
return true;
case 3:
// the object being traversed needs "right" made public
$this->_t2 = $this->_this->right->traverse_inorder();
reset($this->_t2);
$this->_state = 4;
case 4:
if(!($e = each($this->_t2)))
{
$this->_t2 = null;
$this->_state = -1;
return false;
}
$this->_value = $e['value'];
return true;
}
} while(false);
------------------------------------------------------------------------
--
Edit this bug report at https://bugs.php.net/bug.php?id=51460&edit=1