[ruby-core:92273] [Ruby trunk Misc#15723] Reconsider numbered parameters

[merch-redmine@jeremyevans.net]

Issue #15723 has been updated by jeremyevans0 (Jeremy Evans).


dunrix (Damon Unrix) wrote:
> Existing solution for example breaks rule of the general approach, as it only works with (anonymous)blocks and procs, not with lambdas and methods which are strict in arguments. It only adds to fragmentation of the language.

I'm not sure what led you to this statement, as the feature does work with lambdas and methods:


```ruby
lambda{@1+@2}.call(1, 2)
# => 3

lambda{@1+@2}.call(1)
# ArgumentError (wrong number of arguments (given 1, expected 2))

define_method(:a){@1+@2}
a(1, 2)
# => 3

a(1)
# ArgumentError (wrong number of arguments (given 1, expected 2))
```

> Implicit arguments should work universally, ie. also for lambdas and methods.

They do.

> It follows that they have to be independent on presence of explicitly stated arguments.

I do not think that follows, and having both explicit arguments and implicit arguments is more likely to lead to confusion.

> In addition, it requires transparency for all kind of arguments - both positional and keyword incl. "greedy" varargs, with or without default values.

I disagree.  This syntax can make simple blocks even simpler, and simple blocks are much more common than complex blocks.  Implicit block arguments do not have to support all complex cases to be useful.

> Should not clash with existing syntax or scope/identifier naming or even break backwards compatibility.

The syntax was explicitly chosen to be invalid in earlier versions of Ruby, to avoid backwards compatibility issues.  "Clashes with existing syntax" is either false if taken literally (as the syntax is invalid in previous versions of Ruby), or subjective if not taken literally (such as "it doesn't feel right because I am used to @ being only used for instance variables").

----------------------------------------
Misc #15723: Reconsider numbered parameters
https://bugs.ruby-lang.org/issues/15723#change-77606

* Author: sos4nt (Stefan Schüßler)
* Status: Feedback
* Priority: Normal
* Assignee: 
----------------------------------------
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.



-- 
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