Re: Elegant way to return true or nothing from a subroutine?

sub foo {
    return !! shift->{some_obj}->some_method;
}
[download]

or even:

sub foo {
    !! shift->{some_obj}->some_method;
}
[download]

DWIM is Perl's answer to Gödel

Comment on Re: Elegant way to return true or nothing from a subroutine? Select or Download Code

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Re^2: Elegant way to return true or nothing from a subroutine? by monarch (Priest) on Oct 10, 2006 at 15:34 UTC
What does the `!!` mean? I thought it would be not not (in other words, true..)	[reply] [d/l]
Re^3: Elegant way to return true or nothing from a subroutine? by fenLisesi (Priest) on Oct 10, 2006 at 16:00 UTC
Ignoring non-integer values for brevity, the `not not` transformation maps `0` to `0` and everything else to `1`: `my @nums = (-2 .. 2); for my $num (@nums) { printf "!!%2d => %d\n", $num, !!$num; }` [download] gives `!!-2 => 1 !!-1 => 1 !! 0 => 0 !! 1 => 1 !! 2 => 1` [download]	[reply] [d/l] [select]
Re^4: Elegant way to return true or nothing from a subroutine? by ikegami (Patriarch) on Oct 10, 2006 at 16:22 UTC
Not quite. The `not not` transformation maps 0 to false and every other integer to 1. False acts as the nul string in string context, and acts as zero in numerical context. `use warnings; my $false = !!0; my $numzero = 0; my $strzero = '0'; my $nulstr = ''; local $\ = "\n"; print 'false: ', $false; # '' <-- Not zero! print '0: ', $numzero; # '0' print "'0': ", $strzero; # '0' print "'': ", $nulstr; # '' print ''; print 'false: ', 0+$false; # '0' (no warning) print '0: ', 0+$numzero; # '0' (no warning) print "'0': ", 0+$strzero; # '0' (no warning) print "'': ", 0+$nulstr; # '0' with warning` [download] If you wanted something that maps 0 to 0 and every other integer to 1, you'd want `0 + !!$var`. Update: Added $strzero. Minor cosmetic changes.	[reply] [d/l] [select]