From: daniel@...42.com
Date: 2020-04-16T14:07:26+00:00
Subject: [ruby-core:97922] [Ruby master Feature#16670] Reverse order of `expression` in `pattern` for 1-line pattern matching while it's still experimental

Issue #16670 has been updated by Dan0042 (Daniel DeLorme).


I think the `in` syntax and order feels natural when you're actually matching a pattern. It's not AI-like pattern recognition like "find a pattern _in_ this" but rather pattern correspondence like "is this _in_ the range expressed by this pattern".

But when using it only as destructuring assigment it does feel that something is off. Maybe it's because `expr in var` has the opposite order of `for var in expr`.

So rather than reversing the order, I'd like to propose `~|>` as a more natural-feeling alias for rightward destructuring assignment. Full proposal at #16794

----------------------------------------
Feature #16670: Reverse order of `expression` in `pattern` for 1-line pattern matching while it's still experimental
https://bugs.ruby-lang.org/issues/16670#change-85145

* Author: ttilberg (Tim Tilberg)
* Status: Open
* Priority: Normal
----------------------------------------
Currently the 1-line syntax for pattern matching is:

```
# Usage: <expression> in <pattern>

expression = {
  pattern: "Example"
}

expression in {pattern: something}
# something => "Example"
```

Is it technically possible, and desirable to switch the order of this syntax to:

```
# Usage: <pattern> in <expression>

expression = {
  pattern: "Example"
}

{pattern: something} in expression
# something => "Example"

```
?

Here are my reasons:

- It is more intuitive in English -- we are "finding a pattern in something". Finding "something in a pattern" doesn't seem to make sense.
- Assignment is happening, and this keeps assignment on the left side of the operator which feels more natural.
- It matches existing behavior with the workings of the case statement:

Understanding that a `case` block evaluates each `when` expression using `when_expression === case_expression` makes more consistency with `when_pattern in case_pattern` using the new operator.

```
case something
when /pattern/
end

# is equivalent to

/pattern/ === something

# This creates more parity with

case something
in {pattern: x}

# would be equivalent to

{pattern: x} in something
```


Please see the following discussion on Reddit: https://www.reddit.com/r/ruby/comments/favshb/27s_pattern_matching_official_docs_recently_merged/fj2c7ng/



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

Unsubscribe: <mailto:ruby-core-request@ruby-lang.org?subject=unsubscribe>
<http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>