switch removed from the v5.36 feature bundle

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We’re almost at the end of the tragic saga of given-when, a feature added in v5.10. It lost the lexical $_ in v5.24 after that feature was demoted to experimental in v5.14. Smart matching, almost the entire point of given-when, has already been demoted to experimental status. Then, v5.28 flirted with removing given-when before deciding that was too hasty. It’s been awhile, and it’s on to the next step.

The latest humiliation is that the switch feature (really given-when) is longer part of the list of the default features enabled by requiring a version of perl, as in use v5.26;.

The feature is still there if you want to use it, but you need to explicitly enable it:

use feature qw(switch);

But, don’t start using this feature now. You’ve had plenty of time to fix it and you can get most of what you need using for instead.

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.

Continue reading “No more false postfix lexical declarations in v5.30”

Beware of the removal of when in Perl v5.28

[Although I haven’t seen an official notice besides a git commit that reverts the changes, by popular outcry these changes won’t be in v5.28. It’s not that they won’t happen but they won’t be in v5.28. People who depend on Perl should stay vigilant. My advice in the first paragraph stands—change is coming and we don’t know what it is yet.]

Perl v5.28 might do away with when—v5.27.7 already has. Don’t upgrade to v5.28 until you know you won’t be affected by this! This change doesn’t follow the normal Perl deprecation or experimental feature policy. If you are using given-when, stop doing that. If you aren’t using it, don’t start. And everyone should consider if a major change like this on such short notice is comfortable for them. It’s not a democracy but you can still let the core developers know which way you want your favorite language to go.

Continue reading “Beware of the removal of when in Perl v5.28”

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”

Use array references with the array operators

[Update: Perl v5.24 removes this experimental feature]

There’s a significant change in syntax showing up in Perl 5.14. The array operators push, pop, shift, and unshift previously only worked on named arrays or dereferenced references. Now, thanks to David Golden, they’ll work on array references. Not only that, they’ll work on references that you’ve stored in variables or that come as the return values from subroutine calls. This feature will show up in Perl 5.13.7, so you need to compile a development version to try this: Continue reading “Use array references with the array operators”