Issue #15897 has been updated by jeremyevans0 (Jeremy Evans).


mikegee (Michael Gee) wrote:
> > RSpec won't break because their "it" requires an argument
> 
> Unfortunately this is not accurate. RSpec has a shorthand style like this:
> 
> `subject { fortytwo }
> it { is_expected.to eq 42 }`

That's a block argument :).  In any case, the parser treats it differently as NODE_ITER/NODE_FCALL, not as NODE_VCALL:

```ruby
RubyVM::AbstractSyntaxTree.parse("it").children
# => [[], nil, #<RubyVM::AbstractSyntaxTree::Node:VCALL@1:0-1:2>]

RubyVM::AbstractSyntaxTree.parse("it{}").children
# => [[], nil, #<RubyVM::AbstractSyntaxTree::Node:ITER@1:0-1:4>]

RubyVM::AbstractSyntaxTree.parse("it{}").children.last.children
# => [#<RubyVM::AbstractSyntaxTree::Node:FCALL@1:0-1:2>, #<RubyVM::AbstractSyntaxTree::Node:SCOPE@1:2-1:4>]
```

Regarding the proposal itself, the dirtying of the semantics bothers me about this as well.  However, I can see where people would find `it` cleaner than `@` in terms of syntax, so this is really a tradeoff between the cleanliness of semantics and syntax.  I don't have a strong opinion on `it` compared to `@`, but I think either is preferable to `@1` or `_`.

----------------------------------------
Feature #15897: `it` as a default block parameter
https://bugs.ruby-lang.org/issues/15897#change-78338

* 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)


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