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Re: tri-state flags

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Bart Lateur
December 6, 2001 17:32
Re: tri-state flags
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On Wed, 5 Dec 2001 04:32:49 -0500, Michael G Schwern wrote:

>At the risk of being prosaic:
>sub is_false ($) { defined $_[0] && !$_[0] }

Now there's a boring solution.

The other similar solutions offered (although that whole ~ idea is
nice), were equally uninspired I was hoping for something more creative,
something that I had been missing. They were:

	defined($temp = FLAG) && !$temp

Assuming $temp is a lexical, you can't limit it's scope by doing

	defined(my $temp = FLAG) && !$temp

because it's not the same variable. I hate that. Globals, with local, do
the proper thing:

	defined(local $_ = FLAG) && !$_

but it might clash with other uses of $_ in the same scope.

	do { defined(local $_ = FLAG) && !$_ }

doesn't have the disadvantages, but IMO it doesn't look elegant.

Well, I found a slightly unorthodox solution. Just writing a post like
these can be such a source of inspiration... Whether it is elegant or
not, is up to you to decide.

	grep { defined && !$_ } FLAG

in a scalar context... which will return 0 (failure of the test) or 1.
(Do think about the fact that, as is, FLAG will be evaluated in list

I think I like it.


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