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2009年02月18日

any::feature - Backwards-compatible handling of new syntactic features

I've released any::feature. The development repo is on github.

The problem

Perl 5.10 introduces new syntactic features which you can activate and deactivate with the feature module. You want to use the say feature in a program that's supposed to run under both Perl 5.8 and 5.10. So your program looks like this:

use feature 'say';
say 'Hello, world!';

But this only works in Perl 5.10, because there is no feature module in Perl 5.8. So you write

use Perl6::Say;
say 'Hello, world!';

This works, but it's strange to force Perl 5.10 users to install Perl6::Say when the say feature is included in Perl 5.10.

The solution

Use any::feature!

WARNING: This is just a proof-of-concept.

any::feature can be used like Perl 5.10's feature and will try to "do the right thing", regardless of whether you use Perl 5.8 or Perl 5.10.

At the moment, this is just a proof-of-concept and only handles the say feature. If things work out, I plan to extend it with other Perl 5.10 features.

The following programs should work and exhibit the same behaviour both in Perl 5.8 and Perl 5.10.

This program will work:

use any::feature 'say';
say 'Hello, world!';

This program will fail at compile-time:

use any::feature 'say';
say 'Hello, world!';

no any::feature 'say';
say 'Oops';

The features are lexically scoped, which is how they work in Perl 5.10:

{
    use any::feature 'say';
    say 'foo';
}
say 'bar';     # dies at compile-time

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