Feature #21555: Add support for predicate attribute reader names

• Status: Rejected
• Assignee: -
• Target version: -

[shan (Shannon Skipper)]

After manually aliasing predicate methods many times, I wanted to propose letting attr_reader take predicate method names that correspond to instance variables of the base name without a trailing question mark. https://github.com/ruby/ruby/pull/14391

If the base name method doesn't already exist, a predicate name defines a base name method attribute reader to alias then undefines the base name.

For example, this creates an enabled? method that reads @enabled:

attr_reader :enabled?

This feature is only supported for attr_reader and attr, not attr_writer or attr_accessor, since setter methods cannot have question marks.

Example:

class Example
  attr_reader :valid?, :meaning

  def initialize
    @valid = [true, false].sample
    @meaning = 42
  end
end

Example.new.valid? #=> true

[nobu (Nobuyoshi Nakada)]

• Related to Feature #16817: attr_predicate or attr_query or attr_something for ? methods added

[Dan0042 (Daniel DeLorme)]

Also related to #5781 #11167 #12046 #15991 #19708
Popular eh?

[byroot (Jean Boussier)]

This feature is only supported for attr_reader and attr, not attr_writer or attr_accessor, since setter methods cannot have question marks.

Using the same logic, attr_accessor :enabled? could generate #enabled? and #enabled= without problem. attr_writer :enabled? would be weird though.

[nobu (Nobuyoshi Nakada)]

• Is duplicate of Feature #5781: Query attributes (attribute methods ending in `?` mark) added

[nobu (Nobuyoshi Nakada)]

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

[nobu (Nobuyoshi Nakada)]

• Is duplicate of Feature #12046: Allow attr_reader :foo? to define instance method foo? for accessing @foo added

[nobu (Nobuyoshi Nakada)]

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

[nobu (Nobuyoshi Nakada)]

• Is duplicate of Feature #19708: Support `attr_reader :foo?` added

[shan (Shannon Skipper)]

Dan0042 (Daniel DeLorme) wrote in #note-2:

Also related to #5781 #11167 #12046 #15991 #19708
Popular eh?

Wow! There's already an open ticket for this exact issue even. I apologize for not properly searching before filing. I should have just added a PR link there in retrospect.

byroot (Jean Boussier) wrote in #note-3:

This feature is only supported for attr_reader and attr, not attr_writer or attr_accessor, since setter methods cannot have question marks.

Using the same logic, attr_accessor :enabled? could generate #enabled? and #enabled= without problem. attr_writer :enabled? would be weird though.

I was thinking of attr_writer :enabled? being weird and dismissed attr_accessor :enabled?. I didn't think of the case where you want attr_reader :enabled? and attr_writer :enabled without attr_writer :enabled. I wouldn't mind doing an attr_reader :enabled? with attr_writer :enabled but agree attr_accessor :enabled? makes sense based on the pattern.

[matz (Yukihiro Matsumoto)]

• Status changed from Open to Rejected

I still ask you to define def valid? = @valid manually. It is not much worse than attr_reader :valid?.

Matz.

[Dan0042 (Daniel DeLorme)]

I think Matz's position is clear and will not change, so what about closing the related tickets that are still open?