[ruby-core:120063] [Ruby master Feature#20770] A *new* pipe operator proposal

Issue #20770 has been updated by austin (Austin Ziegler).


AlexandreMagro (Alexandre Magro) wrote in #note-52:
> austin (Austin Ziegler) wrote in #note-50:
> > It would *substantially* complicate parsing (one would only want to "assign" `_` if an expression *uses* it), and right now `_` is a valid variable name (if usually used for an unused parameter).
> 
> Using the "last expression result" as a global behavior could introduce unnecessary performance overhead, as the interpreter would need to track and update it for every expression.

Not necessarily. I don't know much about how the parser works to produce the AST, but if it is able to do a *small* bit of backtracking, it could detect the use of `_` (which would otherwise be an "unused variable") and mark the *previous* expression as requiring the last expression result. That would mean that the overhead would only exist when used. This sort of backtracking would be required with the use of `|>` in any case.

> Furthermore, by explicitly using the pipe operator, the "last expression result" gains a clear meaning on its own, and no longer remains just an anonymous placeholder (`_`). This avoids the ambiguity that may arise in the code, which isn't an issue when writing expressions line by line in irb.

I don't entirely agree. The ambiguity still exists because there is (more or less) an implicit block behaviour. If `_` already exists in the current scope, *both* the use of a pipe operator and the implicit "last expression result" would potentially shadow or overwrite the use of `_`. (It may be a silly idea to use a variable called `_`, but it is *legal* to do so right now.)

----------------------------------------
Feature #20770: A *new* pipe operator proposal
https://bugs.ruby-lang.org/issues/20770#change-110801

* Author: AlexandreMagro (Alexandre Magro)
* Status: Open
----------------------------------------
Hello,

This is my first contribution here. I have seen previous discussions around introducing a pipe operator, but it seems the community didn't reach a consensus. I would like to revisit this idea with a simpler approach, more of a syntactic sugar that aligns with how other languages implement the pipe operator, but without making significant changes to Ruby's syntax.

Currently, we often write code like this:

```ruby
value = half(square(add(value, 3)))
```

We can achieve the same result using the `then` method:

```ruby
value = value.then { add(_1, 3) }.then { square(_1) }.then { half(_1) }
```

While `then` helps with readability, we can simplify it further using the proposed pipe operator:

```ruby
value = add(value, 3) |> square(_1) |> half(_1)
```

Moreover, with the upcoming `it` feature in Ruby 3.4 (#18980), the code could look even cleaner:

```ruby
value = add(value, 3) |> square(it) |> half(it)
```

This proposal uses the anonymous block argument `(_1)`, and with `it`, it simplifies the code without introducing complex syntax changes. It would allow us to achieve the same results as in other languages that support pipe operators, but in a way that feels natural to Ruby, using existing constructs like `then` underneath.

I believe this operator would enhance code readability and maintainability, especially in cases where multiple operations are chained together.

Thank you for considering this proposal!






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