Feature #12046: Allow attr_reader :foo? to define instance method foo? for accessing @foo

• Status: Rejected
• Assignee: matz (Yukihiro Matsumoto)
• Target version: -

[mrkn (Kenta Murata)]

Now we should write an accessor method of a boolean instance variable like

def foo?
  @foo
end

But I want to write it by using attr_reader like:

attr_reader :foo?

[nobu (Nobuyoshi Nakada)]

• Is duplicate of Feature #10720: A proposal for something like: attr_reader :foo? - with the trailing '?' question mark added

[shevegen (Robert A. Heiler)]

Yay! Sometimes things just take a while. :)

[matz (Yukihiro Matsumoto)]

• Status changed from Open to Rejected

as a rule, attr_reader x creates an instance variable @x, but we cannot have @x?.
that's the reason, we reject attr_reader :foo?. If you have any concrete use-case for
the new (more complex) behavior, please tell me.

Matz.

[svoop (Sven Schwyn)]

If you have any concrete use-case for the new (more complex) behavior, please tell me.

This feature request has been rejected more than once, so I'm most likely doing this in vain. But the obvious use-case would be better readability. Right now, the way to do it is:

class Foobar
  attr_accessor :color
  attr_writer :transparent
  
  def transparent?
    @transparent
  end
end

Even though the transparent reader is trivial, it has to be explicitly added and thus is not part of the list of other trivial accessors such as color.

If tailing question marks are ignored when trivial writers are created, the code looks as follows:

class Foobar
  attr_accessor :color, :transparent?
end

The writer remains "transparent=", but it could reject any non-boolean values. The reader would be "transparent" with an alias "transparent?"

It's just a little magic to remove crust. And it wouldn't break any existing code because accessors and writers with tailing question marks raise "invalid attribute name" as of now.

[mame (Yusuke Endoh)]

• Related to Feature #11167: Allow an attr_ variant for query-methods that end with a question mark '?' character, such as: def foo? returning @foo added

[mame (Yusuke Endoh)]

• Related to Feature #5781: Query attributes (attribute methods ending in `?` mark) added

[mrkn (Kenta Murata)]

• Related to Feature #15991: Allow questionmarks in variable names added

[byroot (Jean Boussier)]

• Related to Feature #19708: Support `attr_reader :foo?` added

[nobu (Nobuyoshi Nakada)]

• Has duplicate Feature #21555: Add support for predicate attribute reader names added