[ruby-core:86124] [Ruby trunk Feature#13904][Assigned] getter for original information of Enumerator

Issue #13904 has been updated by mrkn (Kenta Murata).

Status changed from Rejected to Assigned
Assignee changed from knu (Akinori MUSHA) to matz (Yukihiro Matsumoto)

Following today's developers meeting, I propose to introduce a subclass of Enumerator.

This is the example implementation of the subclass:

```ruby
class Enumerator::ArithmeticSequence < Enumerator
  attr_reader :first  # already in Enumerator
  attr_reader :last  # newly introduced
  attr_reader :step  # newly introduced

  def inspect
    # appropriate string representation of this class instances
  end
end
```

`Integer#step` and `Range#step` of integer ranges should return the instance of `Enumerator::ArithmeticSequence` like:

```ruby
p 1.step        #=> (1.step)
p 1.step(10)    #=> (1.step(10))
p 1.step(10, 2) #=> (1.step(10, by:2))
p 1.step(by: 2) #=> (1.step(by:2))

p (1..10).step    #=> (1.step(10))
p (1..10).step(2) #=> (1.step(10, by:2))
```

I think introducing this class doesn't introduce incompatibility from the current behaviors, but increase the usefulness of the results of `Integer#step` and `Range#step`.


----------------------------------------
Feature #13904: getter for original information of Enumerator
https://bugs.ruby-lang.org/issues/13904#change-70998

* Author: znz (Kazuhiro NISHIYAMA)
* Status: Assigned
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version: 
----------------------------------------
At https://gitter.im/red-data-tools/ja?at=59b0aaa097cedeb04828e268 ,
mrkn says narray and pycall use internal information of ruby to check `Range#step(n)`.

People of red-data-tools/ja suggest subclass of Enumerator.
But I think it does not match Ruby's '大クラス主義' (I don't know this word in English), so I suggest to add some methods to Enumerator class.

proof of concept attached.

Usage:

```
% irb -r irb/completion --simple-prompt
>> e=(1..2).step(3)
=> #<Enumerator: 1..2:step(3)>
>> e.receiver
=> 1..2
>> e.method_name
=> :step
>> e.arguments
=> [3]
```

`#method` is conflict with `Kernel#method`, so use `#method_name` instead.


---Files--------------------------------
poc.diff (1.42 KB)


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