Effective Perl Programming – write better, more idiomatic Perl
This is a chapter in Perl New Features, a book from Perl School that you can buy on LeanPub or Amazon. Your support helps me to produce more content.
0o prefixtry-catch syntax{,m} regex quantifier\x{...} and {n,m}And, I’ll update the Perl New Features for v5.34 too.
Not all characters with a numerical value are “digits”, in the Perl sense. You saw in Match Unicode characters by property value, in which you selected characters by a Unicode property value. That showed up again in Perl v5.18 adds character class set operations. Perl v5.30 adds a slightly easier way to get at multiple numerical values at the same time. Now you can match Unicode property values with wildcards (Unicode TR 18), which are sorta like Perl patterns. Don’t get too excited, though, because these can be expensive.
Continue reading “Match Unicode property values with a wildcard”
Perl has some of the best Unicode support out there, and it keeps getting better. Perl v5.32 supports Unicode 13, and you can now apply patterns to character names. You probably don’t want to do that though.
First, the Unicode Character Database catalogs each character, giving it a code number, a name, and many other properties.
Continue reading “Match Unicode character names with a pattern”
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.
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.
Continue reading “Chain comparisons to avoid excessive typing”
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.
Continue reading “Use a variable-width lookbehind if it won’t match more than 255 characters”
Perl v5.32 is out and it has some interesting new features. The previous major releases focussed more on finally removing deprecations and shoring up odd cases, and you still find a few of those in this release. Full details, as always, are in the perldelta.
Sawyer X just announced Perl 7 as a major version jump that relabels what is now v5.32. If you’re code is ready for v5.32, you should be mostly ready for Perl 7.
isa infix operator (“class instance”)streamzip program comes with IO::Compress::Base, so it comes with perl"0" .. "-1" is fixed This is a chapter in Perl New Features, a book from Perl School that you can buy on LeanPub or Amazon. Your support helps me to produce more content.
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.
The qr// operator allows you to compile a regular expression without applying it to anything. You get the pattern without the match, and you can reuse the pattern as often as you like. Before v5.30, it had an inconsistency with \N{} sequences, but that’s fixed now.
Continue reading “Perl 5.30 fixes single quoted qr” with \N{}”
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.
Continue reading “No more false postfix lexical declarations in v5.30”