in reply to Re: Re: Re: buffering question
in thread buffering question

It turns out that the value of $| can't be -1. This variable has special magic that only allows its value to be 0 or 1. Any true value assigned to $| becomes 1, and any false value becomes 0. So, $|++ and $|=1 really are interchangeable.

Interestingly, $|-- and $|=0 are not interchangeable. If $| is 1, $|-- will of course set it to 0, but if $| is 0, $|-- will set it to 1!

Similar magic can be found, for example, in the $. variable, which can only hold an integer.

Replies are listed 'Best First'.
Re: Re: Re: Re: Re: buffering question
by Rudif (Hermit) on Aug 29, 2001 at 22:33 UTC
    Thank you, chipmunk, for setting me straight on this one.

    My C upbringing showed up, and I did not test what I presumed was the behavior of $| :-(

    Rudif

    Update </b

    Now that I did test it, turns out to be even more interesting. Running this 

    print $|++ for (0..9);  print"   post ++\n";
print $|-- for (0..9);  print"   post --\n";
print ++$| for (0..9);  print"   pre ++\n";
print --$| for (0..9);  print"   pre --\n";

    [download]
    prints this 
    0111111111   post ++
1010101010   post --
1111111111   pre ++
0101010101   pre --

    [download]
    Creative use of this  $|-- behavior, anyone?

[reply]
[d/l]
[select]
Re: Re: Re: Re: Re: buffering question
by blakem (Monsignor) on Aug 29, 2001 at 07:48 UTC
    Cool, you're right. I just tried it out (should have probably done that *before* I posted) and $| does only ever store the values '0' and '1'.

    Thanks for the correction, I appreciate it.

    -Blake

[reply]
Re: Re: Re: Re: Re: buffering question
by John M. Dlugosz (Monsignor) on Aug 29, 2001 at 08:48 UTC
    Wow, that's good food for an obfu. $_=$|=42;
[reply]
[d/l]

In Section Seekers of Perl Wisdom