[ruby-core:51098] [ruby-trunk - Feature #5781] Query attributes (attribute methods ending in `?` mark)

Issue #5781 has been updated by trans (Thomas Sawyer).


=begin
I revisited this b/c in one of my projects it is much needed. To compensate, I created a special extension called (({attr_switch})),

    def attr_switch(name)
      attr_writer name
      module_eval %{
        def #{name}?
          @#{name}
        end
      }
    end

But it has the problem that the (({#source_location})) for the method created is in attr_switch's definition and not where attr_switch is called. And in my case that is a problem. Does anyone know if there is a way to tell it the (({source_location})) should be at caller[0]? I tried adding that info to (({#module_eval})) call, i.e. 

  file, line = *caller[0].split(':')[0..1]
  module_eval %{...}, file, line.to_i

But it didn't work.

So bringing this back to this feature request. I, for one, still would very much like this feature. Sometimes it's just much more convenient. And I'd much rather it just worked out-of-box then me having to fuss with creating a custom attr method (and as I point out above, I can't even get it to work exactly the same).

I took a look at the relevant C code, (({rb_attr()})) in (({vm_method.c})), but I simply do not understand that code enough to adjust it myself. If I did, I would have submitted a patch for this already.

Given what I understand about the new ((*process*)) for changing Ruby, I guess I need a sponsor from core team or a core member of another implementation. Is that correct? If so, is anyone willing to back this?
=end

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Feature #5781: Query attributes (attribute methods ending in `?` mark)
https://bugs.ruby-lang.org/issues/5781#change-35033

Author: trans (Thomas Sawyer)
Status: Assigned
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: 
Target version: next minor


Pretty sure this has come up before, but I'd like to revisit b/c I don't understand why it isn't allowed.

Sometimes I define "query" attributes, and in those cases I'd like the reader method to end in a `?` mark. Currently I have to do:

    # @attribute
    def foo?
      @foo
    end

or, if I don't mind a shadowing bare method,

    attr :foo
    alias_method :foo?, :foo

So why not just allow:

    attr :foo?

Currently this causes an error. But why? It just seems like a waste of potentially cleaner code.


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