Add applied_attribute as a possible role metarole

[gitmo/Moose.git] / TODO

== Todo for 2.0400

=== RT Tickets

RT#67731 - Union types reports spurious parent types -
https://rt.cpan.org/Ticket/Display.html?id=67731

RT#59478/RT#63000 - 0+ overload causes NV conversion on == on perls before
5.14 - this causes comparisons to fail when the number can't fit in an NV
without precision loss. I'd like to fix this in a more general way (forcing
anyone else who might be using == on tc objects to do weird things isn't very
good), although it's hard to test to see what actually works.

RT#69839 - UNIVERSAL methods should show up as methods, so things like method
modifiers work

=== Revise MetaRole API to reunify class/role metaroles:

  apply_metaroles(
      for   => $meta,
      roles => {
          attribute => [...],
          class     => [...],
          role_attribute => [ ... ],
      }
  );

If the $meta is a class, we apply the roles to the class. If it's a role, we
hold onto them and apply them as part of applying the role to a class.

To make this all work nicely, we'll probably want to track the original role
where a method was defined, just like we do with attributes currently. We'll
also need to store method modifiers with their original role, which may mean
adding some sort of Moose::Meta::Role::MethodModifier class.

For each role-specific thing (methods, attributes, etc.) we should allow a
role_attribute, role_method, etc. key. The common case will be that the
metaroles are intended for the consuming class, but we should allow for
metaroles on the role's metaobjects as well.

=== Deprecate old-style Moose extensions

Moose extensions that work by calling Moose->init_meta(metaclass =>
'Some::Custom::Metaclass', ...) during their own init_meta should be
deprecated, so they can be removed later (this should fix the issues with
init_meta generation in Moose::Exporter, see RT51561)

=== Register implicitly created class/role types

When you do has foo => (isa => 'Bar'), it returns a class_type for Bar, but
doesn't register it. This means that later you can declare "subtype 'Bar', as
'Str', ..." and it'll work, and later instances of the 'Bar' type will use that
one. We should register the implicitly created ones so that trying to redefine
it after it's used throws an error.

=== Attributes in roles need to be able to participate in role composition

Right now, this fails with no decent workaround:

  package R1;
  use Moose::Role;
  has foo => (is => 'ro');

  package R2;
  use Moose::Role;
  with 'R1';
  requires 'foo';

  package C;
  use Moose;
  with 'R2';

Role attributes really need to be able to participate in role-role combination.
This should also fix "with 'Role1', 'Role2'" being broken when Role1 implements
a method as an accessor and Role2 requires that method, but at least in that
case you can split it into two 'with' statements with minimal loss of
functionality.

=== Method modifiers in roles should silently add 'requires' for them

This shouldn't be a functionality change, just a better error message (and
better introspectability). This shouldn't happen if the role already contains a
method by that name, so it'll depend on the previous fix going in (so "has foo
=> (is => 'ro'); around foo => sub { }" doesn't produce a 'requires' entry).

=== Add overloading support

or at least, don't break existing overloading support

This shouldn't treat the overloading stuff as actual methods, since that's just
an implementation detail, but we should provide an API for add_overload,
get_overload, get_overload_list, etc. In particular, this would allow
namespace::autoclean to not break things.

Also, MooseX::Role::WithOverloading should probably be cored.


== Todo for later

=== Actual API for metaclass extensions

Right now, the only way to bundle multiple metaclass traits is via
Moose::Exporter. This is unhelpful if you want to apply the extension to a
metaclass object rather than a class you're actually writing. We should come up
with an API for doing this.

=== MooseX::NonMoose in core

I think all of the actual issues are solved at this point. The only issue is
the (necessary) implementation weirdness - it sets up multiple inheritance
between the non-Moose class and Moose::Object, and it installs a custom
constructor method at 'extends' time (although perhaps this could be solved by
moving some of the logic back into Moose::Object::new?). Other than that, it
handles everything transparently as far as I can tell.

=== Fix attribute and method metaclass compatibility

So i got this wrong when rewriting it last year - right now, metaclass compat
checks the default attribute and method metaclasses, which is wrong. This means
that if a parent class does "use MooseX::FollowPBP", then attributes declared
in a subclass will get PBP-style accessors, which is quite surprising.

On the other hand, sometimes metaclasses might need to be able to say "I'm
going to assume that all of my attributes at least inherit from this custom
class", so we might need to split it into "default specified by the user" and
"default specified by the metaclass" and only do compat checking on the second?
I'm not actually sure this is a valid use case though.

Something that probably should be taken into account though is attributes and
methods that extend existing attributes or methods from a superclass should
inherit the metaclass of the existing one. Also not sure if this is correct,
but something to think about.

=== Rename a bunch of the public API methods

Right now the public API is kind of a mess - we have things like get_method vs
find_method_by_name (you almost always want to use the latter), there being no
has_method equivalent that checks superclasses, get_method_list being public
but only returning method names, while _get_local_methods is private (returning
method objects), and yet neither of those looks at superclasses, and basically
none of this naming follows any kind of consistent pattern.

What we really need is a consistent and easy to remember API where the method
that people would think to use first is the method that they actually mean.
Something like renaming find_method_by_name to find_method, and get_method to
find_local_method or something along those lines.

=== Move load_class and related stuff out to an external module

Choices include Class::Load, Module::Runtime, or writing something ourselves.
Module::Runtime doesn't currently support is_class_loaded, and neither of those
two support load_first_existing_class, and we have is_class_loaded in XS at the
moment, because we call it enough internally (mostly by load_class) for it to
be noticeable.

=== Move method modifiers out to an external module

Class::Method::Modifiers uses a different method for doing method modifiers,
which I'm not sure why we aren't using in Moose right now. Optionally using
Class::Method::Modifiers::Fast would be even better - it uses Data::Util to
implement XS method modifiers, which could help things a lot.

=== Move type constraints out to an external module

There's nothing about our type constraint system that requires being tied to
Moose - it's conceptually an entirely separate system that Moose just happens
to use. Splitting it out into its own thing (that Moose could extend to add
things like role types) would make things conceptually a lot cleaner, and would
let people interested in just the type system have that.

=== Merge Class::MOP and Moose

This is a long term goal, but would allow for a lot of things to be cleaned up.
There's a bunch of stuff that's duplicated, and other stuff that's not
implemented as well as it could be (Class::MOP::Method::Wrapped should be a
role, for instance).


== Things to contemplate

=== Does applying metaroles really need to reinitialize the metaclass?

Seems like the logic that's actually necessary is already contained in
rebless_instance, and not reinitializing means that existing attributes and
methods won't be blown away when metaroles are applied.

=== Do we want to core namespace::autoclean behavior somehow?

This would add Variable::Magic as a required XS dep (not a huge deal at the
moment, since Sub::Name is also a required XS dep, but it'd be nice for Moose
to be able to be pure perl again at some point in the future, and I'm not sure
what the relative chances of Sub::Name vs Variable::Magic making it into core
are). If we enabled it by default, this would also break things for people who
have introduced Moose into legacy-ish systems where roles are faked using
exporters (since those imported methods would be cleaned).

If we decide we want this, we may want to core it as an option first ("use
Moose -clean" or so), and move to making it the default later.

=== Fix the error system

oh god it's terrible

More specifically, we really want exception objects.

=== Should using -excludes with a role add 'requires' for excluded methods?

It seems to make sense, since otherwise you're violating the role's API
contract.


== Old todo (does anyone look at this?)

-------------------------------------------------------------------------------
BUGS
-------------------------------------------------------------------------------

-------------------------------------------------------------------------------
FEATURES
-------------------------------------------------------------------------------

- DDuncan's Str types

subtype 'Str'
    => as 'Value'
    => where { Encode::is_utf8( $_[0] ) or $_[0] !~ m/[^0x00-0x7F]/x }
    => optimize_as { defined($_[0]) && !ref($_[0]) };

subtype 'Blob'
    => as 'Value'
    => where { !Encode::is_utf8( $_[0] ) }
    => optimize_as { defined($_[0]) && !ref($_[0]) };

- type unions

Add support for doing it with Classes which do not have
a type constraint yet created

- type intersections

Mostly just for Roles

- inherited slot specs

'does' can be added to,.. but not changed
(need type unions for this)

- proxy attributes

a proxied attribute is an attribute
which looks like an attribute,
talks like an attribute, smells
like an attribute,.. but if you
look behind the curtain,.. its
over there.. in that other object

(... probably be a custom metaclass)

- local coerce

[13:16] 	mst	stevan: slight problem with coerce
[13:16] 	mst	I only get to declare it once
[13:17] 	mst	so if I'm trying to declare it cast-style per-source-class rather than per-target-class
[13:17] 	mst	I am extremely screwed
[13:17] 	stevan	yes
[13:17] 	stevan	they are not class specific
[13:18] 	stevan	they are attached to the type constraint itself
[13:18] 	*	stevan ponders anon-coercion-metaobjects
[13:18] 	mst	yes, that's fine
[13:19] 	mst	but when I declare a class
[13:19] 	mst	I want to be able to say "this class coerces to X type via <this>"
[13:19] 	stevan	yeah something like that
[13:19] 	stevan	oh,.. hmm
[13:20] 	stevan	sort of like inflate/deflate?
[13:20] 	stevan	around the accessors?
[13:25] 	*	bluefeet has quit (Remote host closed the connection)
[13:27] 	mst	no
[13:27] 	mst	nothing like that
[13:27] 	mst	like a cast
[13:31] 	mst	stevan: $obj->foo($bar); where 'foo' expects a 'Foo' object
[13:31] 	mst	stevan: is effectively <Foo>$bar, right?
[13:32] 	mst	stevan: I want to be able to say in package Bar
[13:32] 	mst	stevan: coerce_to 'Foo' via { ... };
[13:32] 	mst	etc.
[13:53] 	stevan	hmm

-----------------------------------------------------------
-- Type Constraints refactor
-----------------------------------------------------------

- add support for locally scoped TC

This would borrow from MooseX::TypeLibrary to prefix the TC with the name
of the package. It would then be accesible from the outside as the fully
scoped name, but the local attributes would use it first. (this would need support
in the registry for this).

- look into sugar extensions

Use roles as sugar layer function providers (ala MooseX::AttributeHelpers). This
would allow custom metaclasses to provide roles to extend the sugar syntax with.

(NOTE: Talk to phaylon a bit more on this)

- allow a switch of some kind to optionally turn TC checking off at runtime

The type checks can get expensive and some people have suggested that allowing
the checks to be turned off would be helpful for deploying into performance
intensive systems. Perhaps this can actually be done as an option to make_immutable?

- misc. minor bits

* make the errors for TCs use ->message
* look into localizing the messages too
* make ANON TCs be lazy, so they can possibly be subsituted for the real thing later
* make ANON TCs more introspectable
* add this ...

#
#   Type Definition
#
subtype 'Username',
   from 'Str',
  where {     (/[a-z][a-z0-9]+/i or fail('Invalid character(s)'))
          and (length($_) >= 5   or fail('Too short (less than 5 chars)'))
        }
on_fail { MyException->throw(value => $_[0], message => $_[1]) };

# fail() will just return false unless the call is made via
$tc->check_or_fail($value);

* and then something like this:

subtype Foo => as Bar => where { ... } => scoped => -global;
subtype Foo => as Bar => where { ... } => scoped => -local;

# or

subtype Foo => as Bar => where { ... } => in __PACKAGE__ ;

# or (not sure if it would be possible)

my $Foo = subtype Bar => where { ... };

# ----------

[17:10]  <autarch> stevan: it should do it if I pass coerce => 1 as part of the attribute definition
[17:12]  <stevan> autarch: what I am not 100% sure of is how to tell it to deep coerce and when to not
[17:13]  <stevan> cause a basic coerce is from A to B
[17:13]  <autarch> hmm
[17:13]  <stevan> which is valid for collection types too
[17:13]  <stevan> deep coercion is what you are asking for
[17:13]  <autarch> yeah
[17:13]  <stevan> so perhaps we add deep_coerce => 1
[17:13]  <stevan> which will do it
[17:13]  <autarch> that's fine for me
[17:13]  <stevan> k

coerce_deeply => 1 # reads better

-------------------------------------------------------------------------------
INTERNALS
-------------------------------------------------------------------------------

- rationalize all the get_X methods for classes (and roles)

We have get_attribute, get_attributes_list, get_all_attributes,
etc. First, we need to make the method names consistent. If something
returns an attribute vs a name, that needs to be clear from the method
name. We also need to make sure that local vs. "entire inheritance
chain" is clear from the name.

This is mostly a CMOP change.

- Metaclass constructors

There's a _lot_ of different conventions in here. Some things to consider:

* new vs _new
* allowing new( 'name', %args ) vs ( name => 'name', %args )
* Method->wrap vs Method->new

- Moose::Meta::TypeConstraint::Parameter{izable,ized}

The relationship between these two classes is very odd. In particular,
this line in Parameterized is insane:

    foreach my $type (Moose::Util::TypeConstraints::get_all_parameterizable_types()) {

Why does it need to loop through all parameterizable types? Shouldn't
it know which parameterizable type it "came from"?

- Moose::Util::TypeConstraints vs Moose::Meta::Type{Coercion,Constraint}

The Util module has _way_ too much functionality. It needs to be
refactored so it's a thin sugar layer on top of the meta API. As it
stands now, it does things like parse type names (and determine if
they're valid), manage the registry, and much more.

- Anything with a _(meta)?class method

Every method that returns a class name needs to become a rw attribute
that can be set via the constructor.

- The Moose::Error stuff

This is sort of half-implemented. We still use Carp directly, and the
internals can't decide how to throw an error (is it
Moose->throw_error, __PACKAGE__->throw_error, what?).

The internals need to be made consistent before we expose this to the
rest of the world.

-------------------------------------------------------------------------------
TO PONDER
-------------------------------------------------------------------------------

- Moose "strict" mode

use Moose 'strict'; This would allow us to have all sort of expensive tests
which can be turned off in prod.

- Moose::Philosophy.pod

To explain Moose from a very high level

- moosedoc

We certainly have enough meta-information to make pretty complete POD docs.