Turn off indirect object notation

Perl v5.32 adds a way to turn off a Perl feature that you shouldn’t use anyway. You can still use this feature, but now there’s a way to take it away from you. And, with the recent Perl 7 announcement, we see why. Eventually Perl wants to get rid of indirect object notation (and I explain that more in Preparing for Perl 7.

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Chain comparisons to avoid excessive typing

Checking that a value is between two others involves two comparisons, and so far in Perl that’s meant that you’ve had to type one of the values more than once. That gets simpler in v5.32 with chained comparisons. This would make Perl one of the few languages that support the feature. So far its implemented in v5.31.10 and until v5.32 is actually released, it isn’t a real feature.

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Use a variable-width lookbehind if it won’t match more than 255 characters

In Ignore part of a substitution’s match, I showed you the match resetting \K—it’s basically a variable-width positive lookbehind assertion. It’s a special feature to work around Perl’s lack of variable-width lookbehinds. However, v5.30 adds an experimental feature to allow a limited version of a variable-width lookbehind.

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Use the infix class instance operator

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This feature is stable in v5.36

Perl v5.32 adds Paul Evans’s infix isa operator—the “class instance operator” as an experimental feature. It still has some issues to work out which prevent its use at the moment, but it looks promising. It subverts how the UNIVERSAL::isa does its job and breaks that in the process. As an experimental feature, that’s fine, but you shouldn’t use this until that’s worked out.

There’s no word on versions for can or does.

One of the delightful things to note about this is addition is that it is one of the features whose development took place almost entirely through a GitHub issue and pull request. GitHub is now the primary repository for the Perl code, and has been since October 2019. This is a feature that I’ll want to use right away in new production code.

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No more false postfix lexical declarations in v5.30

Before Perl v5.10 introduced state variables, people did various things to create persistent lexical variables for a subroutine. With v5.30, one of those constructs is now a fatal error.

Often you want a persistent variable to be scoped and private to a subroutine. But, once you leave that scope, normal lexical variables disappear because their reference count drops to zero. So, no persistence.

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Match only the same Unicode script

Earlier this year, this website was the target of some sort of attack in which a bot sent seemingly random data in its requests. The attack wasn’t that big of a deal since I easily blocked it with Cloudflare, but it was interesting. The apparently random data was actually a mix of Latin, Hangul, and Cyrillic. Domain hacks with unusual Unicode characters shows some of these exploits. Curiously, v5.28 added some regex feature that deals with this sort of nonsense.


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Use atomic matching for complex non-backtracking

You can sometimes improve the performance of your regular expression by preventing parts of it from backtracking when you know that might be useful. Item 38. Avoid unnecessary backtracking had many techniques for this, although it did not mention atomic matching (a feature added in v5.005).

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Use alpha assertions for more understandable regexes

[This feature stabilizes in Perl v5.32]

Perl v5.28 adds more-readable, alternate spelled-out forms for some of its regular expression extended patterns. Then, to make those slightly less readable, there are very short initialisms for those. Although these might seem superfluous now, the ability to define new syntax without relying on the limited number of ASCII symbols.

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Perl v5.30 lets you match more with the general quantifier

Does the {N,} really match infinite repetitions in a Perl regular expression? No, it never has. You’ve been limited to 32,766 repetitions. Perl v5.30 is about to double that for you. And, if you are one of the people who needed more, I’d like to hear your story.

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