From: "Ara.T.Howard" <ahoward@...>
Date: 2003-11-22T01:27:19+09:00
Subject: Re: "stereotyping" (was: Re: Strong Typing (Re: Managing metadata about attribute types) )

On Sat, 22 Nov 2003, Mark Wilson wrote:

> My own views on interface crystallization:

(similar to my own)

> 1. It should not be done in-line, but rather through a separate express
> creation of an interface table. [Note: one of the nice things about the way
> Ruby (and other languages) does things is the inline creation of dispatch on
> type tables for generic operators through the use of classes in an object
> system. It would be bad to complicate this and other elements of Ruby's
> human interface by also putting interface "contracts" inline with Ruby's
> current (usually very comprehensible) class declaration system.]

i thinks it's absolutely in line with the ruby way for an 'interface' to
simply be an object

class Interface
  def initialize object = nil
    skeletonize object if object
  end
end

> 2. The table would include fields specifying whether the interface is
> mutable or immutable, the number of arguments and "types" of arguments a
> method takes, exceptions to raise if the particular interface element fails,
> and so on.

this too, should simply be an object

class Interface
  attr :signatures
  class Signature
    def initialize object = nil, meth = nil  
      skeletonize object, meth if object and meth
      @signatures = Hash.new # map meth name to signature
    end
  end
end

> 3. A skeleton table could be generated from existing code, with suitable
> default values (such as mutable interface, argument "type" set to Object,
> etc. The developer would choose where to crystallize an interface element
> and forego additional possible dynamism.

skeleton_sig = Signature.new Array, :each

class Interface
  class Signature
    # true/false
    def takes_block; end

    # attributes of block
    def block_attr; end

    # list of errors/exceptions types
    def raises; end

    # list of Classes, Interfaces, or methods any argument must respond_to?
    # example: sig.signature # => [String, StringInterface, :to_s]
    def signature; end
  end
end


> 4. The table could be queried to produce detailed documentation information
> and/or included at runtime as a constraint on execution.

see above

> 5. In the future, one could perhaps also use the table to guide a Ruby
> compiler as to when a form of "static typing" can be used to optimize a
> particular program (according to the instructions of the developer).


6. Interfaces __HAVE__ implementations vs. classes __IMPLEMENTING__ an
Interface.  this is vastly simpler with respect to backward compat:

  BAD:

    class MyClass
      # requires change to class 'Class'
      implements Interface
    end

  GOOD:

    interface.impl << MyClass

    # no change to class 'Class' needed


> I do not, however, think the proposal is necessarily a good idea. It 
> does seem very costly, and the magnitude of the benefit is not clear to 
> me. A way to make it lower-cost would be good, because then it would be 
> easier to try.


again, agreed.  but if people HAVE to have such a beast i concur that it
should be a completely separate one - not tightly intergrated into the
language.


> Some questions:
<snip>

> How can Ruby better document the kind of block code that would be 
> useful with respect to a particular method?

perhaps

  class Interface
    class Signature; end
    class MethodSignature < Signature; end
    class BlockSignature < Signature; end
  end

???

<snip>

-a
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