Re: Get even postion elements in an array

[LanX]

$a=1;print grep {$a=1-$a} @input

or, more cryptic

$a=1;print grep {$a^=1} @input

[happy.barney]

@output = @input[ grep $_ & 1, 0 .. $#input];

($mod, $val) = (2, 1);
@output = @input[ grep $_ % $mod == $val, 0 .. $#input];

[anonymized user 468275]

Why not be LESS cryptic, e.g.:-

my $flipflop = 1;
my @result = grep { $flipflop = not $flipflop; }, @input;

[LanX]

I prefer reusable idioms.

Here not is indeed more readable, but it won't produce 0 for false, which could be counterintuitive in other cases.

$flipflop needs to be declared, while $a (and $b) is already global as part of the sort idiom, which is a similar case of using a code block.

$a=1;
my @result = grep { $a = not $a }, @input;

At the end it's a matter of taste. ^= is shorter, = not is clearer, but =1- can equally be used in most other languages, making it an universally understood idiom.

[anonymized user 468275]

Reusable idioms are an open block to your thinking. They are not the same as reusable code. '' is just as false as 0 and is often preferable -- for example, a routine returns or sets a scalar by reference originating from a unix exit code, 0 being unix success, so '' is the best value for "i had to abort earlier than that" $a is not a global, it's a special variable for use in sort blocks, that shouldn't be abused especially by habit -- one day a sort routine will come back to bite you in the bottom. Are you trying to say that not declaring locally and instead using global variables is a virtue? Many here will disagree.

[LanX]

for completeness, an application of the new state feature for implicit initialization and scoping:

  DB<23> use feature "state"; print grep { state $ff ^= 1 } 0..9
02468
  DB<24> use feature "state"; print grep { not state $ff ^= 1 } 0..9
13579