[ruby-core:20221] Re: Proposal: deferred blocks

My example was only a real-use that already exists.
You articulated the problems with your approach (namely, it falls apart when
you hit language constructs). People have been playing with this for a
while, but a big blocker is the fact that it's known not to work outside of
1.8.x MRI.

As I clarified earlier, I'm not asking for ParseTree functionality in Ruby.
I'm asking for procs to optionally remember their string form so that they
can be processed by other utilities (like RubyParser). It's not as intensive
as requiring that Ruby have a standard AST across implementations, and might
potentially have other benefits (error handling, for instance).

-- Yehuda

On Tue, Dec 2, 2008 at 10:47 AM, Florian Gilcher <[e-mail]>wrote:

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> Hi Yehuda,
>
> Is this really necessary?
>
> I've been playing alot with instance_exec and and fake objects and have
> been able to mimic at least such basic stuff without resorting to using the
> parsetree.[1] You can get a long way with that, as long as you don't hit
> true language constructs (|| and such).
>
> I still have my issues with parstree-hackery and don't see the point why we
> desperatly need it - especially in core Ruby. Also, I don't see the point of
> most examples for this, including yours. Ruby will never be SQL. If you want
> to query in Ruby, use a language that takes Ruby-code as query language.
> parsetree-hackery depends on a feature of the interpreter that is not at all
> standardized.
>
> To show you an example how your specific problem can easily be solved with
> more-than-plain Ruby is attached - it takes more work to bring it the whole
> way. Be aware that you should use some kind of BlankSlate-Object for this,
> but for example-reasons, I left it out. It also only cares about this really
> specific example.
>
> Regards,
> Florian Gilcher
>
> P.S.: If i see this in dm-core, i'll stop using DM. And that would be tough
> for me.
>
> [1]: For those who saw my talk about Patterns on EuRuKo 2008: yes, for
> this. Sadly, still unreleased.
>
> ==Code==
>
> class SelectProxy < BasicObject
>  attr_accessor :model, :queried_attribs
>
>  def initialize(model)
>   @model = model
>   @queried_attribs = {}
>  end
>
>  def method_missing(selector, *args)
>   if @model.attributes.include? selector
>     self.queried_attribs[selector] ||= ::AttributeProxy.new(selector)
>   end
>
>   #if not, do something else
>  end
>
>  #this is totally bad, but for the sake of an example...
>  def compile
>   tablename = @model.name.downcase
>   conditions = queried_attribs.values.map do |attribute|
>                   attribute.queries.join(" AND ")
>                end.join(" AND ")
>   "SELECT * FROM #{tablename} WHERE #{conditions}"
>  end
> end
>
> class AttributeProxy
>  attr_accessor :attribute, :queries
>
>  def initialize(attribute)
>   @attribute = attribute
>   @queries = []
>  end
>
>  def =~(arg)
>   @queries << "#{self.attribute} ~ '#{arg.source}'"
>  end
>
> end
>
> class Article
>  #lets assume we can get a list of attributes on class level
>  class << self
>   attr_accessor :attributes
>  end
>
>  self.attributes = [:title, :body]
>
>  def self.select(&block)
>   proxy = SelectProxy.new(self)
>   proxy.instance_exec &block
>   return proxy.compile
>  end
> end
>
> puts Article.select { title =~ /Some title/ }
>
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>


-- 
Yehuda Katz
Developer | Engine Yard
(ph) 718.877.1325