Issue #15897 has been updated by Hanmac (Hans Mackowiak).
`_` can't be used as default block parameter because it already has a special meaning when using block variables like `{|a,_,_,b| }`
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Feature #15897: `it` as a default block parameter
https://bugs.ruby-lang.org/issues/15897#change-78326
* Author: mame (Yusuke Endoh)
* Status: Open
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version:
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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)
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