From: Ara.T.Howard@...
Date: 2005-05-04T12:04:49+09:00
Subject: Re: [ANN] traits-0.0.0

On Tue, 3 May 2005, Kevin Howe wrote:

> Very cool, this is along the lines of something I've been toying with for
> the next version of Nemo (rubyforge.org/projects/nemo). Nemo tags class
> attributes (traits) with display-related metadata, then later uses it to
> render an html table or html edit form. The trait version might look
> something like this:
>
>  class Foo
>    mtrait :name, :label=>'Full Name', :required=>true
>    mtrait :birthday, :type=>:date, :required=>true
>  end
>
>  foo = Foo.new
>  foo.name = 'Joe'
>  foo.birthday = Date.today
>
>  Editor.new(foo).render
>
> This would display an html form with two required text fields labelled "Full
> Name" and "Birthday". Hitting the save button updates the object instance
> with the given input, assuming it passes all validations.

so mtrait would be a wrapper on trait?

> I've been wanting to abstract out the metadata definition into a generic
> mechanism for defining metadata on any attribute, but if this were added to
> traits that would pretty much be it. Thoughts?

you would want something like

   class Foo
     trait 'a', 'description' => 'metadata', 'fu' => 'bar'
   end

   p Foo::trait_opts('a')

that'd be possible.  or did you mean something else?

> Also, how does trains handle inheritance? Let's say we have A < B, then B
> adds a few more traits, will A's @__trait data remain unaffected?

it handles it.  it's __very__ tricky however since

   - can't use @@var since derived classes will clobber
   - can't use @var since each class will simply have own

so instead it uses @vars with a search_path up ancestors.  this turns out to
be kinda tricky in the general case....

eg.

   jib:~/eg/ruby > cat a.rb
   require 'traits'

   class A
     trait 'a'
   end

   p A::traits

   class B < A
     trait 'b'
   end

   p B::traits

   p A::traits


   jib:~/eg/ruby > ruby a.rb
   [["a"], ["a="]]
   [["b", "a"], ["b=", "a="]]
   [["a"], ["a="]]


cheers

-a
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