Dynamic properties and has_key? check.

[Jamie Hill]

Hi,

Apologies if this is a stupid question. I would like a Ruby object to have dynamic properties based on certain conditions, am I safe to define a '[]' method and return values from there? If so, how would I return an 'undefined' value as 'nil' just translates to 'null'. I'm wondering if the code here https://github.com/cowboyd/therubyracer/blob/master/lib/v8/access/names.rb#L13-15 should perform a check first i.e:

elsif obj.respond_to?(:[]) && obj.has_key?(name) && !special?(name)

...that way I could simple override 'has_key?' as well as the '[]' method. Here is a code example of what I'm doing currently but need to know how to return 'undefined':

require 'v8'

class Proxy

  def [](name)

    # How to return undefined?

    return nil unless stuff.include?(name)

    

    define_singleton_method(name) do

      name.upcase

    end.call

  end

  

  private

  

  def stuff

    %W(foo bar)

  end

end

class Root

  def proxy

    Proxy.new

  end

end

context = V8::Context.new(with: Root.new)

puts context.eval("'foo: ' + proxy.foo + ', bar: ' + proxy.bar + ', baz: ' + proxy.baz")

Thanks in advance.

[Charles Lowell]

Jamie,

You can return undefined by yielding. This will tell your definition to not handle the call at all, and it will proceed up the prototype chain. e.g.

def [](name)

  if stuff.include? name

    # do stuff

  else

    yield

  end

end

cheers,

Charles

-- 
Charles Lowell

@cowboyd

http://frontside.io

http://github.com/cowboyd

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