$i = $i ++; Its behaviour is undefined.

It is defined. The ++ operator has nothing to do with this, in Perl. You're right about perlop, and with multiple increments/decrement the order in which things happen is undefined (well, not always. But it is not clear either). But that isn't really what we're dealing with. This is an assignment, just like any $i = EXPR. In this case, EXPR is $i++, which causes $i to be incremented, but returns the old value. The value of EXPR is assigned to $i, so as an end result nothing happens. If $i is tied, FETCH, STORE and STORE are called. 

$i = 5;
$i = $i++;
print $i, "\n"; # 5\n

[download]
  1. $i is set to 5
  2. $i is incremented, new value is 6
  3. old value (5) is used as the rhs of the assignment operator
  4. $i is set to that value, old value was 6, new value is 5
  5. $i and newline are printed 
$i = 5;
$i = ++$i;
print $i, "\n"; # 6\n

[download]
  1. $i is set to 5
  2. $i is incremented, new value is 6
  3. new value (6) is used as the rhs of the assignment operator
  4. $i is set to that value, old value was 6, new value is 6
  5. $i and newline are printed

I have tried this with Perl 5.005 and 5.6.1.

Note: I agree that $i = $i++ is bad style and should never ever be used in non-obfu. 

- Yes, I reinvent wheels.
- Spam: Visit eurotraQ.

In reply to Re: Re: Incrementing a Hash Value by Juerd
in thread Incrementing a Hash Value by arunhorne

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