From: hanmac@...
Date: 2018-08-10T13:09:49+00:00
Subject: [ruby-core:88438] [Ruby trunk Feature#14609] `Kernel#p` without	args shows the receiver

Issue #14609 has been updated by Hanmac (Hans Mackowiak).


ko1 (Koichi Sasada) wrote:
> Hanmac: do you rely on this behavior?

Me? not so much, in general i don't trust the return value of print commands (print returns null)

it was months ago, i probably wanted to point out that the return value of `p` might be differ depending on the parameters
It might be inconsistency?


There is `Object.display` too but i don't use it much because it doesn't have new lines

----------------------------------------
Feature #14609: `Kernel#p` without args shows the receiver
https://bugs.ruby-lang.org/issues/14609#change-73493

* Author: ko1 (Koichi Sasada)
* Status: Open
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version: 2.6
----------------------------------------
# Abstract

`Kernel#p(obj)` prints obj as `inspect`ed.
How about to show the receiver if an argument is not given?

# Background

We recently introduce `yield_self` which encourages block chain.

https://zverok.github.io/blog/2018-01-24-yield_self.html
Quoted from this article, we can write method chain with blocks:

```
construct_url
  .yield_self { |url| Faraday.get(url) }.body
  .yield_self { |response| JSON.parse(response) }
  .dig('object', 'id')
  .yield_self { |id| id || '<undefined>' }
  .yield_self { |id| "server:#{id}" }
```

There is a small problem at debugging.
If we want to see the middle values in method/block chain, we need to insert `tap{|e| p e}`.

With above example,

```
construct_url
  .yield_self { |url| Faraday.get(url) }.body
  .yield_self { |response| JSON.parse(response) }.tap{|e| p e} # debug print
  .dig('object', 'id')
  .yield_self { |id| id || '<undefined>' }.tap{|e| p e} # debug print
  .yield_self { |id| "server:#{id}" }
```

# Proposal

`obj.p` shows same as `p(obj)`.

We can replace
  `block{...}.tap{|e| p e}`
to 
  `block{...}.p`

For above example, we can simply add `.p` at the end of line:

```
construct_url
  .yield_self { |url| Faraday.get(url) }.body
  .yield_self { |response| JSON.parse(response) }.p # debug print
  .dig('object', 'id')
  .yield_self { |id| id || '<undefined>' }.p # debug print
  .yield_self { |id| "server:#{id}" }
```

# Compatibility issue

(1) Shorthand for `nil`

This spec change can introduce compatibility issue because `p` returns `nil` and do not output anything.
That is to say, `p` is shorthand of `nil`. Some code-golfers use it.

Maybe we can ignore them :p

(2) make public method

`Kernel#p` is private method, so if we typo `obj.x` to `obj.p` (not sure how it is feasible), it will be `NoMethodError` because of visibility.
We need to change this behavior.

# Note

## Past proposal and discussion

Endoh-san proposed same idea 10+ years ago [ruby-dev:29736] in Japanese.
I think we should revisit this idea because of `yield_self` introduction.

At this thread, Matz said "simple `p` shows `p(self)`, it is not clear".

[ruby-dev:30903]

```
  p

���������������������������(p self���������������������������)

  self.p(obj)

���������������������������������������������(������)������������������������������������
```

English translation:

```
What the behavior of (I feel strange that it is similar to `p(self)`):

  p

What happen on

  self.p(obj)
```

## pp

If this proposal is accepted, we also need to change `pp` behavior.

## gems

`tapp` method is provided by gem.
https://github.com/esminc/tapp 

I'd thought to propose this method into core. But I found that `p` is more shorter than `tapp`.
Disadvantage is `p` is too short and difficult to grep.




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