Effective Perl Programming – write better, more idiomatic Perl
Perl v5.20 introduced key-value slices that worked on hashes and arrays. You could extract values by their keys or indices as well as assigning to those.
The key-value slice delete is way to extract the keys and values you want and delete them at the same time. You can destructively
Continue reading “Perl v5.28 can delete key-value slices”
Subroutine signatures, in a rudimentary form, have shown up in Perl v5.20 as an experimental feature. After a few of years of debate and a couple of competing implementations, we have something we can use. And, because it was such a contentious subject, it got the attention a new feature deserves. They don’t have all the features we want (notably type and value constraints), but Perl is in a good position to add those later. Continue reading “Use v5.20 subroutine signatures”
Perl 5.20 introduced experimental subroutine signatures. Now two features vie for the parentheses that come after the name in a subroutine definition. To get around that, v5.20 introduced the :prototype attribute.
There’s not much to this. Here’s a prototype for a subroutine that takes two arguments:
sub add ($$) { ... }
Change that to the attribute form:
use v5.20;
sub add :prototype($$) { ... }
But, you probably don’t need prototypes in the first place. You might consider simply getting rid of them altogether.
Subroutine signatures are experimental and have to go through at least two maintenance releases before they can graduate out of an experimental feature, so be ready for that. I expect that most people will have problems with module code they don’t control, so you might be at the mercy of the module maintainers.
Perl v5.20 fixes taint checking in regular expressions that might use the locale in its pattern, even if that part of the pattern isn’t a successful part of the match. The perlsec documentation has noted that taint-checking did that, but until v5.20, it didn’t.
The only approved way to untaint a variable is through a successful pattern match with captures: Continue reading “Perl v5.20 fixes taint problems with locale”
[Update: This feature became stable in Perl v5.24]
Perl v5.20 offers an experimental form of dereferencing. Instead of the complicated way I’ll explain in the moment, the new postfix turns a reference into it’s contents. Since this is a new feature, you need to pull it in with the feature pragma (although this feature in undocumented in the pragma docs) (Item 2. Enable new Perl features when you need them. and turn off the experimental warnings: Continue reading “Use postfix dereferencing”
Perl v5.20 continues to clean up and optimize its internals. Now perl optimizes a series of lexical variable declarations into a single list declaration. Continue reading “Perl v5.20 combines multiple my() statements”
Perl was once known for its one-liners in its sysadmin heydays. People would pass around lists of these one liners, many of which replaced complicated pipelines that glued together various unix utilities to do some impressive system maintenance. Continue reading “In v5.20, -F implies -a implies -n”
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””
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”
Prior to v5.20, perl used whatever random number generator the system provided. This meant that the same program could have statistically different results based on the quality of that function. The rand() for Windows had a max of 32,768 (15 bits), while POSIX has drand48 (48 bits). This sort of numerical un-portability has always been a problem with perl since it’s relied on the underlying libc for so much. Continue reading “Perl 5.20 uses its own random number generator”