Description

I have a module I currently call List::Extract that has a single subroutine: extract. It's used like

my @extracted = extract { ... } @list;
[download]

It removes and returns the elements that tests true for the code in the block, like grep and splice combined. The code above is equivalent to

my @extracted;
my $c = 0;
while ($c < @$list) {
    local *_ = \$list->[$c];
    if (do { ... }) {
        push @extracted, splice @$list, $c, 1;
    }
    else {
        $c++;
    }
}
[download]

Motivation

The reason I wrote this routine was that I haven't found any idiom to achieve the same thing that I'm pleased with. The only other way that I'm lazy enough to write that's significally shorter and logically simpler than the code above is

my @extracted = grep { ... } @list;
@list = grep { not ... } @list;
[download]

but I don't like that, mostly because it duplicates the logic in the grep block, and factoring it out would make it unpretty again:

my $filter = sub { ... };
my @extracted = grep { $filter->() } @list;
@list = grep { not $filter->() } @list;
[download]

and still I iterate the array twice.

My questions

• Is there any other module that does the same thing? (I haven't found any on CPAN.)
• Do you have any suggestion for a better name?
• Do you think that modifications to $_ should be discarded for elements in the returned list?
• Do you think that modifications to $_ should be discarded for elements kept in the array?

lodin

Update: Uploaded as List::Extract to CPAN.

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