[ruby-core:92154] [Ruby trunk Misc#15723] Reconsider numbered parameters

[psychoslave@culture-libre.org]

Issue #15723 has been updated by psychoslave (mathieu lovato stumpf guntz).


Hello Matthew! You wrote:

> The argument against the feature is people who don't want to use it, who inherit code (one way or another) from people who did use it and are therefore forced to use it.  If you don't see it, it doesn't hurt you.

I don't think that's the main point here, at least to my mind it's . Readability, consistency and lake of surprise are the main concern here. The `@` prefix coming in semantic conflict with the already used for instance variable is the most worrying point, to my mind.

This morning I woke up with this idea in mind: maybe we could use a letter suffix.

Sticking to English custom and habit regarding ordinal number notation, the proposal could take the form of this arguments could become : `1st`, `2nd`, `3rd`, `4th`, `5th`, and so on. This as the obvious con of irregularity on the three firsts that are most likely being the most used. Also a bit longer than the arobase prefix equivalent. The pro however is that it should make sense to anyone with a basic knowledge of English.

An other proposal would be to use a single letter. For example using `a` as suffix, you end up with `1a`, `2a`, `3a` and so on. Fully regular, as short to type as the arobase prefixed version, and I guess conflict-free with other use of the letter, as well as backward compatible. Bonus, `-a` is actually used to form ordinal number in Esperanto! Ok, I don't expect this last one to come as a strong point, but it's funny to note that. One con with this option would be that one could at first be confused that `1a` actually stands for `0x1a` (26). But once you have the notation in mind it's not more problematic than `1e3` (1000, engineering notation). At worst you can always peak any other letter out of the [a-f] range.

Cheers.

----------------------------------------
Misc #15723: Reconsider numbered parameters
https://bugs.ruby-lang.org/issues/15723#change-77481

* 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.



-- 
https://bugs.ruby-lang.org/