Category Archives: 5.12

Don’t use auto-dereferencing with each or keys

Perl 5.14 added an auto-dereferencing features to the hash and array operators, and I wrote about those in Use array references with the array operators. I’ve never particularly liked that feature, but I don’t have to like everything. Additionally, Perl 5.12 expanded the job of keys and values to also work on arrays. chromatic has [...]

Use Test::More as you experiment

When you’re trying something new, write small programs to test the idea or the new feature. This way, you isolate what you’re doing from the rest of the big application where you might want to use the idea. Some people try to insert the new features directly into the middle of their large programs, but [...]

Use the \N regex character class to get “not a newline”

Perl 5.12 introduced an experimental regex character class to stand in for every character except one, the newline. The \N character class is everything but the newline. In prior versions of Perl, this is the same thing as the . meta character. That is, it’s the same as long as someone doesn’t add the /s [...]

Use a smart match to match several patterns at once

The smart match operator (Item 23. Make work easier with smart matching) reduces many common comparisons to a few keystrokes, keeping with Perl’s goal of making the common things easy. You can use the smart match operator to make even less common tasks, such as matching many regular expressions at the same time, just as [...]

In Perl v5.12, length(undef) returns undef.

Starting with v5.12, the length of an undefined value is undefined itself. Instead of converting the undef to the empty string then taking the length of that string, v5.12 returns undef: $ perl5.10.1 -le ‘print defined length(undef) ? “Defined” : “undef”‘ Defined $ perl5.12.1 -le ‘print defined length(undef) ? “Defined” : “undef”‘ undef When you [...]

Use when() as a statement modifier

Perl 5.10 introduced the given-when statement, and Perl 5.12 refines it slightly by letting you use the when as a statement modifier. A statement modifier puts the conditional expression at the end of the statement (see perlsyn). You’ve probably already used many of these: print “It’s too darned hot!\n” if $city eq ‘Baltimore’; print “I’m [...]

Temporarily remove hash keys or array elements with `delete local`

Perl 5.12 adds a feature that lets you locally delete a hash key or array element (refresh your memory of local with Item 43: Know the difference between my and local. This new feature allows you to temporarily prune a hash or an array: delete local $hash{$key}; delete local $array[$index]; This syntax has actually been [...]

Implicitly turn on strictures with Perl 5.12

Perl 5.12 can turn on strict for you automatically, stealing a feature from Modern::Perl that takes away one line of boilerplate in your Perl programs and modules. We talk about strict in Item 3: Enable strictures to promote better coding. Similar to what we show in Item 2: Enable new Perl features when you need [...]

Turn off Perl 5.12 deprecation warnings, if you dare!

Perl 5.12 deprecates several features, for various reasons. Some of the features were always stupid, some need to make way for future development, and some are just too ornery to maintain. All of these are listed in the perldelta5120 documentation. The new thing, however, is that Perl 5.12 will warn you about these even if [...]

Watch out for side effects with `use VERSION`

To specify that you wanted to use at least a particular version of Perl, you specified that version with the use built-in: use VERSION; We covered this in Item 83: Limit your distributions to the right platforms, and we mentioned that it might invoke side effects. We didn’t get into the details in that Item [...]