Issue #15897 has been updated by shevegen (Robert A. Heiler).


Just a very brief comment since it was discussed in the last developer meeting, solely on the
syntax issue of %1, %2, versus @1, @2 and :1, :2:

To me personally, %1, %2 is almost the same as @1, @2. I'd still prefer @1 @2 etc... but I
don't have a huge problem with %1, although I find @1 more elegant than %1, purely syntax-wise.

The idea for :1, :2 on the other hand, though, looks somewhat strange to me.

It reminds me more of a symbol than @1 reminds me of an instance variable, oddly enough.

If @1 would not be considered to be good from a syntax point (although I find it just
fine), then I think %1 would be better than :1.

To those who would like to have a look at the developer meeting log, the summary was
provided by mame (I think) here:

https://docs.google.com/document/d/1K61SGIwp8_rNsPyhmayUcERu71vt_etDjXdhqrLmBVY/edit#

----------------------------------------
Feature #15897: `it` as a default block parameter
https://bugs.ruby-lang.org/issues/15897#change-79301

* Author: mame (Yusuke Endoh)
* Status: Open
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version: 
----------------------------------------
How about considering "it" as a keyword for the block parameter only if it is the form of a local varaible reference and if there is no variable named "it"?

```
[1, 2, 3].map { it.to_s } #=> ["1", "2", "3"]
```

If you are familiar with Ruby's parser, this explanation is more useful: NODE_VCALL to "it" is considered as a keyword.

Examples:

```
public def it(x = "X")
  x
end

[1, 2, 3].map { it.to_s }    #=> ["1", "2", "3"]
[1, 2, 3].map { self.it }    #=> ["X", "X", "X"] # a method call because of a receiver
[1, 2, 3].map { it() }       #=> ["X", "X", "X"] # a method call because of parentheses
[1, 2, 3].map { it "Y" }     #=> ["Y", "Y", "Y"] # a method call because of an argument
[1, 2, 3].map { it="Y"; it } #=> ["Y", "Y", "Y"] # there is a variable named "it" in this scope

it = "Z"
[1, 2, 3].map { it.to_s }    #=> ["Z", "Z", "Z"] # there is a variable named "it" in this scope
```

Pros:
* it is the best word for the feature (according to @matsuda)
* it is reasonably compatible; RSpec won't break because their "it" requires an argument

Cons:
* it actually brings incompatibility in some cases
* it is somewhat fragile; "it" may refer a wrong variable
* it makes the language semantics dirty

Fortunately, it is easy to fix the incompatible programs: just replace `it` with `it()`.  (Off topic: it is similar to `super()`.)
Just inserting an assignment to a variable "it" may affect another code.  This is a bad news, but, IMO, a variable named "it" is not so often used.  If this proposal is accepted, I guess people will gradually avoid the variable name "it" (like "p").
The dirtiness is the most serious problem for me.  Thus, I don't like my own proposal so much, honestly.  But it would be much better than Perlish `@1`.  (Note: I don't propose the removal of `@1` in this ticket.  It is another topic.)  In any way, I'd like to hear your opinions.


An experimental patch is attached.  The idea is inspired by @jeremyevans0's [proposal of `@`](https://bugs.ruby-lang.org/issues/15723#note-98).


P.S. It would be easy to use `_` instead of `it`.  I'm unsure which is preferable.

---Files--------------------------------
its.patch (4.92 KB)
mame_its_proposal.patch (5.26 KB)


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