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Re: Pre-RFC: a `library` keyword

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Ovid via perl5-porters
April 1, 2022 15:28
Re: Pre-RFC: a `library` keyword
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Fair enough everyone. I'll stop beating this horse :)
Best,Ovid-- IT consulting, training, specializing in Perl, databases, and agile development 
Buy my book! - 

    On Friday, 1 April 2022, 16:16:49 CEST, Paul "LeoNerd" Evans <> wrote:  
 On Fri, 01 Apr 2022 09:54:37 -0400
"Ricardo Signes" <> wrote:

> Item 5 is good.  We should try to eliminate the need for "magic true
> value" in v5.38, generally.

Indeed; I think last time when we discussed the previous iteration of
the idea ("module"), we said that overall everything can be already
solved by the `use VERSION` and `package NAME VERSION {BLOCK}` features
that already exist in Perl and have done for a very long time, apart
from two small additions of:

 * A mechanism (maybe attribute?) to request per-function lexical

 * A named feature that causes the .pm file as a whole to yield a true
  value at the end.

I forget what we called them but those could be spelled:

  use feature qw(export_attr yield_true);

  package Some::Module v1.23 {
    sub this_is_exported :export { ... }

    sub this_method_is_not { ... }

    my sub this_is_lexically_private { ... }

  # no need for "1;" here because of the yield_true feature

That can all work *right now* with the `package` keyword. Furthermore,
the two new features, once implemented, could become part of a
`use VERSION` bundle at some future version of perl, so you could
simply write

  use v5.100;  # has already enabled strict, warnings, signatures and
              #  yield_true; has disabled indirect, etc...

  package Some::Module v1.23 {
    sub f :export ($x, $y) { ... }

Looking further over the (closed) PR from last time:

What I said was:

  @Ovid I think the :export attribute could stand alone well in its own
  RFC. Do you want to write one up, or should I?

  A couple of further thoughts on it:

  * Perl core already reserves all the lowercase attribute names for
    its own future expansion. There's no need to use feature-guard it.
    We can add `:export` right now.

  * I think the named tags should take a leading colon; e.g.
    `:export(:strings)`. That way they visually match what the
    `use Module ':strings';` import line looks like, and also it gives
    us some space to put other options in there one day.

I would definitely be in favour of seeing (two?) RFCs to specifically
add these ideas:

  1. An :export attribute for lexical exports (see quoted PR comment

  2. A `use feature 'yield_true'` to avoid having to put "1;" at the end
    of the file; with a future plan to include that by default in the
    versioned feature bundles.

I believe that combination, plus a proper understanding of how
`use VERSION` and `package NAME VERSION {BLOCK}` already work in Perl,
will fully cover the use-cases and benefits of your proposed "library"
keyword, without the need for new keywords or a significant departure
of existing Perl syntax.

Paul "LeoNerd" Evans      |  |
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