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Roles are fundamentally broken?

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From:
Vadim Belman
Date:
January 29, 2019 02:03
Subject:
Roles are fundamentally broken?
Message ID:
11A21DDB-7316-4A05-9CD5-29CAA79DA25F@lflat.org
Hi all,

I have filled another role-related issue today. While the issue is just another bug in the compiler, it stems from the thing which I consider to be a big problem about what a Role is in Perl6. Or, more precisely, from the fact that Role is an entity deprived of its civil rights.

What functionality would I expect from a Role? Two things:

1. Define interfaces
2. Define abstract behaviors

What Perl6 is currently providing me with? Interfaces – ok; behaviors – only partially. For example, there is no guarantee that a BUILD or TWEAK submethod defined in a Role would ever be run, unless a class does special measures to ensure them be executed.

What I expect a Role to be? Perhaps, more of a degraded Class in a way that roles would be able to participate in MRO resolution, for example. In a way that roles must be able to participate in object initialization process equally to classes; after all, isn't this a part of object behavior too?

If somebody would like to object by saying that "Role isn't a Class" then think about punning first.

Not to mention the ability of declaring per-role 'our' objects which is not critical but would be handy sometimes.

Having the roles to be so special seemingly causes lots of unwanted side effects and bugs. For example, https://github.com/rakudo/rakudo/issues/2657, https://github.com/rakudo/rakudo/issues/2496, and https://github.com/rakudo/rakudo/issues/2282 just wouldn't exists with roles being part of MRO. An attribute object would probably have its .package attribute set correctly. And couple of other issues.

Basically, at this moment I consider carefully if I need a role or there is another way to implement something. Because what is known for sure now: there will be problems, sooner or later!

Maybe somebody could explain clearly why things are the way they are now. I would be very thankful for such information. Perhaps I need a tectonic shift in my understanding of this area. But currently roles are the only thing which really disappoints me in the language design.

Best regards,
Vadim Belman

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