Perl v5.20 adds the “Key/Value Slice”, which extracts multiple keys and their corresponding values from a container (hash or array). It uses the %, which is new, legal syntax for a variable name with subscripts after it: Continue reading “Perl 5.20 introduces “Key/Value Slices””
Category: chapters
Perl 5.20 optimizes return at the end of a subroutine
Want to save 10 nanoseconds? Perl v5.20 optimizes a return at the end of a subroutine to use two fewer ops in the optimized version. During compilation, a subroutine like this one: Continue reading “Perl 5.20 optimizes return at the end of a subroutine”
Declare packages outside of their block
Perl v5.14 gets a step closer to a saner way to declare classes with its new package NAME BLOCK syntax that lets you easily group everything that goes in a package. Continue reading “Declare packages outside of their block”
Experimental features now warn (reaching back to v5.10)
Perl 5.18 provides a new way to introduce experimental features in a program, augmenting the feature pragma that v5.10 added. This change marks certain broken v5.10 features as experimental with an eye toward possible removal from the language.
Smart matching in v5.10 led to several broken and conflated features. The given used a lexical version of $_, which broke many other common uses of that variable inside the given, which I explain in Use for() instead of given() and you can see in given/when and lexical $_ …. Continue reading “Experimental features now warn (reaching back to v5.10)”
The vertical tab is part of \s in Perl 5.18
Up to v5.18, the vertical tab wasn’t part of the \s character class shortcut for ASCII whitespace. No one really knows why. It was curious trivia that I pointed out in Know your character classes under different semantics. Whitespace in ASCII, POSIX, and Unicode represented different sets. Perl whitespace was different from POSIX whitespace by only the exclusion of the vertical tab. Now that little oversight is fixed. Continue reading “The vertical tab is part of \s in Perl 5.18”
Ignore part of a substitution’s match
Normally, a substitution replaces everything it matched, but v5.10 adds a feature that allows you to ignore part of the match. The \K excludes from $& anything to its left. This feature has already made it into PCRE. It doesn’t have an official name, so I’ll call it the match reset operator because it resets the start of $&.
The Perl 5.12 yada yada operator
Perl v5.12 adds a placeholder operator, ..., called the yada yada operator, after an episode of Seinfeld where the interesting parts of the story are replaced with “yada yada yada”. Continue reading “The Perl 5.12 yada yada operator”
Hide namespaces from PAUSE
The Perl Authors Upload Server (PAUSE) is responsible for analyzing distributions on their way to CPAN. PAUSE indexes the distributions to discover the package names that it contains so it can add them to the data files that many of the CPAN clients use to figure out what to download to install the module that you request. It also compares the package names that it finds to a list of permissions it maintains. Continue reading “Hide namespaces from PAUSE”
Don’t use auto-dereferencing with each or keys
[Update: Perl v5.24 removes this experimental feature, for the reasons I list, among others.]
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. Continue reading “Don’t use auto-dereferencing with each or keys”
Look up Unicode properties with an inversion map
Perl comes with extracts of the Unicode character data, but it hasn’t been easy to look up all of the information Perl knows about a character. Perl v5.15.7 adds a way to created an inverted map based on the property that you want to access.
Continue reading “Look up Unicode properties with an inversion map”