[ruby-core:41757] Re: [ruby-trunk - Feature #5781] Query attributes (attribute methods ending in `?` mark)

[Anurag Priyam <anurag08priyam@gmail.com>]

On Tue, Dec 20, 2011 at 8:17 PM, Jeremy Bopp <jeremy@bopp.net> wrote:
> How about adding an attr_query method that otherwise works identically
> to attr_reader but creates a method with a '?' on the end of the given
> name instead?

I would suggest the name `predicate` instead.

class Foo
  attr :bar
  predicate :bar
end

Alternatively,

On Tue, Dec 20, 2011 at 7:33 PM, Yukihiro Matsumoto <matz@ruby-lang.org> wrote:
> The other option is removing '?' from instance variables.  But as far as I remember no one seriously proposed the idea before, and we haven't got consensus.

Use `attr`, but if the variable name passed to `attr` contains a '?'
define a predicate corresponding to it too.

class Foo
  attr :bar?
  attr :baz
end

f = Foo.new
f.bar?  #=> nil
f.bar = 'meh'
f.bar    #=> 'meh'
f.bar?  #=> 'meh'

f.baz?  #=> NoMethodError

The predicate could be made to strictly return `true` or `false`
instead of simply behaving like an attribute reader.


The former is perhaps easier to implement, but I would like to use the
latter approach in my code.

-- 
Anurag Priyam