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

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

[shevegen (Robert A. Heiler)]

Hi guys,

Hi nobu :)

Also hi matz if matz reads this, and of course the rest of the core
team and everyone else.

Today on IRC, this mini-discussion happened (I show a snippet):

<apeiros> I really miss attr_query or whatever you want to name it
<apeiros> which would generate a ? method too
<jhass> apeiros: crystal has :P getter?
<apeiros> nice

Ok, so the language crystal has something ruby does not have.

We can't let those newcomers get away with making ruby look old
now can we!

I use ruby not crystal but I very often use methods that end
with a '?' query mark in ruby. It helps me in simple if clauses
such as:

if hash.has_key?
if hash.key?
if cat.is_hungry?

(In the latter, it might be a cat of class Cat instance, with
an instance variable called @is_hungry, and when the cat is
fed with food, it is not hungry logically.)

We can generate these @ivars through attr_* right now as is
already, such as:

attr_reader :foo
def foo; @foo; end

attr_writer :foo
def foo=(i); @foo = i; end

attr_accessor :foo
^^^ Combines the above two methods into one.

But we have no way to designate methods that end via '?'.

I do not know which API call would be nice. apeiros on
IRC suggested attr_query

I am fine with that. (The name is secondary for me, I
would like to have this feature available - what name
it would then have is not the main issue for me.)

apeiros then also suggested this syntax:

All attr_* that would end with a ? token, would be a
combination of attr_reader and also a variant of the
above that has a '?' token, so for example:

attr_reader :foo?

Would create both a method foo() and foo?().

People who do not need this, can continue to use:

attr_reader :foo

just fine.

So perhaps this suggestion is even better than
a new method (such as through attr_query())

(I also have added one more line from apeiros,
not sure if I understood it, but I think the
above explanation should suffice - here is the
other suggestion he did:)

apeiros> e.g. attr_reader :foo? -> foo? // attr_accessor :foo? -> foo= + foo? // all with @foo of course. and foo? returning true/false.

Ok, that's it.

Thanks for reading!

[nobu (Nobuyoshi Nakada)]

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

[nobu (Nobuyoshi Nakada)]

• Description updated (diff)

[matz (Yukihiro Matsumoto)]

Hi,

Is there any real-world use-case for the proposal?
It seems

  def foo?
    @foo
  end

is just fine.

Matz.

[djberg96 (Daniel Berger)]

Abandoned all hope:

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-core/5796

https://www.ruby-forum.com/topic/135195

[spatulasnout (B Kelly)]

Hi Matz,

Yukihiro Matsumoto wrote:

Is there any real-world use-case for the proposal?

I've wanted this feature for years. :)

Here's an example from code I'm working with today:

  def startup_complete?
    @startup_complete
  end

I would have preferred:

  attr_reader :startup_complete?

It seems

  def foo?
    @foo
  end

is just fine.

Perhaps fine, but clunky. :)

In other words, why do we ever use attr_reader (etc.) at all?

We use attr_.* because it's preferable to writing a bunch of
mini-functions.

The reasons are identical for the '?' variant.

Regards,

Bill

[duerst (Martin Dürst)]

Daniel Berger wrote:

Abandoned all hope:

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-core/5796

https://www.ruby-forum.com/topic/135195

I think that this shows that there are several people who really like to use a foo? getter with a foo= setter. What it doesn't show that there are enough such people that it would balance out the confusion for those who think that a foo= setter goes together with a foo getter, at least by default.

With the current state, the main case is covered, nobody gets confused, and those who want a foo?/foo= pair can easily get it either as Matz showed above (easily reduced to one line) or by redefining the attr_... methods; the later is also very easy as it is usually about the first example given when explaining metaprogramming.

[matz (Yukihiro Matsumoto)]

• Status changed from Open to Rejected

See #12046.

Matz.

[mame (Yusuke Endoh)]

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

[anders (Anders Bälter)]

Like that!

sudo (Sudo Nice) wrote:

How about implementing it similarly to Crystal?

attr_accessor? :foo

https://bugs.ruby-lang.org/issues/5781#note-16

[nobu (Nobuyoshi Nakada)]

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