In response to:
----------------------
T Chan
19-Aug-2006 10:30
[...]
In response to the manual, associativity doesn't determine
the order of evaluation - it determines how it's
"bracketed": a=b=c=1 is equivalent to a=(b=(c=1)),
but a is evaluated first (an important point if evaluating a
has side-effects)
<?php
function one($str) {
echo "$str";
return 1;
}
$a = array(1,2);
$a[one("A")] = $a[one("B")] = 1; //
outputs AB
?>
----------------------
The manual, stated "associativity determines order of
evaluation," which is completely correct, as it uses a
stack execution, as with C.
The example you provided to counter the manual's statement
however, is contrived, as it uses function calls to output a
variable which is not even used in assignment; this in turn
disproves (in your opinion) the manual's statement. Fuction
calls, have much higher precedence than the assignment
operator.
However:
Right Associativity with the '=' operator means the
following:
The expression: $a = $b = 1;
IS indeed evaluated from right to left.
The stack is used as follows. (if you're not familiar with
stacks / queues, look em up).
The expressions are pushed onto the stack in the following
order:
$a $b = 1 =
^ ^
Bottom Top
The stack is then "evaluated" from top to bottom
(which translates from right to left, if you're reading the
expression)
It would read: assign 1 to assign $b to $a
Which results in $a = 1
Try the following simple script:
<?php
function output(& $b)
{
echo( "b value is: ".$b );
return $b;
}
$a = 2;
$b = 5;
echo ($a = $b = 1);
$a = 2;
$b = 5;
echo ( "a value is: ".$a = output($b) );
?>
Output is:
1
b value is: 5
a value is: 5
---------------------------------------
Your example had nothing to do with the assignment operator
evaluation order, only procedural precedence.
----
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Probable Submitter: 24.121.21.115
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