Re: Common Perl Idioms

[Anonymous Monk]

Some of the ones I can remember off the top of my head...

# slurp a bunch of files
@files = { local(@ARGV, $/) = @filenames; <> };

# get the indexes of items in an array
@foo{ @foo } = 0 .. @foo;
$foo{'abc'} # the index of 'abc' in @foo

# Get the sign of a number
$a <=> 0

# test primality
sub isPrime { (1 x $_[0]) !~ /^(11+)\1+$/ }
# (ok I never use that in production code
#   but it is funny)

Ted

[revdiablo]

Your slurp:

    @files = { local(@ARGV, $/) = @filenames; <> }; # missing 'do'

Should actually be:

    @files = do { local(@ARGV, $/) = @filenames; <> };

And your index hash:

    @foo{ @foo } = 0 .. @foo; # off-by-one error

Should be:

    @foo{ @foo } = 0 .. $#foo;

[Anonymous Monk]

You are right about the slurp, a typo on my part.

But the indexing will work. The extra number (int @foo) will just be ignored because there won't be a corresponding lvalue.

Ted :->

[I0]

1 is not prime. Neither is 0.

[davorg]

# Get the sign of a number
$a <=> 0

Or just use "abs".

Ignore me. I'm talking nonsense.

[adrianh]

Or just use "abs".

Eh?

[Anonymous Monk]

The @foo{ @foo } = 0 .. @foo; seems very clever to me (not to mention useful), but being a bit of a newbie, I don't really understand how it works. Anyone care to enlighten me?

[Eimi Metamorphoumai]

It's creating a hash named %foo using a hash slice built out of the elements in @foo. Then it's assigning to that slice the values 0 to (the number of elements). So if @foo = ('a', 'b', 'c'), you get

@foo{'a', 'b', 'c'} = (0, 1, 2);

which is itself just shorthand for

$foo{'a'} = 0;
$foo{'b'} = 1;
$foo{'c'} = 2;

(technically, @foo in scalar context returns a value one too large, so we're really mapping to (0,1,2,3), but the odd element gets ignored. It might be more proper to use $#foo there (the index of the last element, instead of the number of elements))

[Anonymous Monk]

Aaaaaaaah... That was clever. Thanks!

[dragonchild]

You want to look up hashslices. That's going to be the key.