Feature #16828
Updated by sawa (Tsuyoshi Sawada) almost 4 years ago
I propose to add find pattern patterns to pattern matching. # Specification ``` find_pattern: Constant(*var, pat, ..., *var) | Constant[*var, pat, ..., *var] | [*var, pat, ..., *var] ``` This pattern is patterns are similar to array pattern, except that patterns, but it finds the 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, that it doesn't support backtracking to avoid complexity, complexity. This means that the proposed feature doesn't support backtracking. Thus, the following code raises a NoMatchingPatternError. ```ruby case [0, 1, 2] in [*, a, *] if a == 1 end ``` # Implementation * https://github.com/k-tsj/ruby/tree/find-pattern-prototype