Issue #16828 has been updated by Dan0042 (Daniel DeLorme).


From the implementation linked above:

```ruby
case [0, 1, 2]
in [*, a, *] 
  p a #=> 0; non-greedy match
end

case [0, 1, 2]
in [*, b, 2, *]
  p b #=> 1; backtracking
end
```

So yes, it supports "backtracking" in a certain fashion otherwise the second case wouldn't match.

Note that it only supports splat expressions at the beginning and end of the array:

```ruby
case [0, 1, 2, 3, 4, 5, 6]
in [*, a, *, b, 5, *] 
  p a, b
end
# syntax error, unexpected ',', expecting ']'
# in [*, a, *, b, 5, *]
```


----------------------------------------
Feature #16828: Introduce find patterns
https://bugs.ruby-lang.org/issues/16828#change-85840

* Author: ktsj (Kazuki Tsujimoto)
* Status: Open
* Priority: Normal
----------------------------------------
I propose to add find patterns to pattern matching.

# Specification
```
find_pattern: Constant(*var, pat, ..., *var)
            | Constant[*var, pat, ..., *var]
            | [*var, pat, ..., *var]
```

This patterns are similar to array patterns,
but it finds first match values from the given object.

```ruby
case ["a", 1, "b", "c", 2, "d", "e", "f", 3]
in [*pre, String => x, String => y, *post]
  p pre  #=> ["a", 1]
  p x    #=> "b"
  p y    #=> "c"
  p post #=> [2, "d", "e", "f", 3]
end
```

Note that it doesn't support backtracking to avoid complexity.
This means that the following code raises NoMatchingPatternError.

```ruby
case [0, 1, 2]
in [*, a, *] if a == 1
end
```

# Implementation
* https://github.com/k-tsj/ruby/tree/find-pattern-prototype




-- 
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>