From: michaur@...
Date: 2019-07-14T11:20:19+00:00
Subject: [ruby-core:93756] [Ruby master Misc#15723] Reconsider numbered	parameters

Issue #15723 has been updated by mihao (Micha�� Kosek).


I have used `@1` a bit in different code snippets and in the great majority of cases there is only one argument and "1" really feels out of place. I definitely support `@`, or anything else without a number.

That said, there's still a way to support several arguments in the cases where they make sense. In Scala, you can write:

    List(1,2,3).foldLeft(1){ _ * _ }

How about using similar syntax in Ruby?

    [1,2,3].reduce{@ * @} # => 6

If you need to repeat the same variable twice, you shouldn't use unnamed arguments, so I think it's better to interpret two `@` as two different arguments.

But then again, perhaps `_` would be better than `@` here? `_` is the only name that can occur several times in the list of named arguments, so using `_` to mean subsequently unnamed argument1, unnamed argument2, etc. would be something kinda related. Just an idea. 

----------------------------------------
Misc #15723: Reconsider numbered parameters
https://bugs.ruby-lang.org/issues/15723#change-79395

* Author: sos4nt (Stefan Sch����ler)
* Status: Feedback
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
----------------------------------------
I just learned that *numbered parameters* have been merged into Ruby 2.7.0dev.

For readers not familiar with this feature: it allows you to reference block arguments solely by their *index*, e.g.

```ruby
[1, 2, 3].each { |i| puts i }

# can become

[1, 2, 3].each { puts @1 }
```

I have an issue with this new feature: I think **it encourages sloppy programming** and results in **hard to read code**.

---

The [original proposal](https://bugs.ruby-lang.org/issues/4475) was to include a special variable (or keyword) with a **readable name**, something like:

```ruby
[1, 2, 3].each { puts it }

# or

[1, 2, 3].each { puts this }
```

Granted, that looks quite lovely and it actually speaks to me ��� I can *understand* the code. And it fits Ruby: (quoting the website)

> [Ruby] has an elegant syntax that is natural to read and easy to write.

But the proposed `it` / `this` has limited application. It's only useful when dealing with a single argument. You can't have multiple `it`-s or `this`-es. That's why `@1`, `@2`, `@3` etc. were chosen instead.

However, limiting the usefulness to a single argument isn't bad at at. In fact, a single argument seem to be the limit of what makes sense:
```
h = Hash.new { |hash, key| hash[key] = "Go Fish: #{key}" }

# vs

h = Hash.new { @1[@2] = "Go Fish: #{@2}" }
```
Who wants to read the latter? That looks like an archaic bash program (no offense). We already discourage Perl style `$`-references: (from [The Ruby Style Guide](https://github.com/rubocop-hq/ruby-style-guide#no-perl-regexp-last-matchers))

> Don't use the cryptic Perl-legacy variables denoting last regexp group matches (`$1`, `$2`, etc). Use `Regexp.last_match(n)` instead.

I don't see how our code can benefit from adding `@1` and `@2`.

Naming a parameter isn't useless ��� it gives context. With more than one parameter, naming is crucial. And yes, naming is hard. But avoiding proper naming by using indices is the wrong way.

So please reconsider numbered parameters.

Use a readable named variable (or keyword) to refer to the first argument or ditch the feature entirely.

---Files--------------------------------
implicit-param.diff (20 KB)


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