From: "zverok (Victor Shepelev)" Date: 2022-02-12T20:22:53+00:00 Subject: [ruby-core:107564] [Ruby master Feature#18583] Pattern-matching: API for custom unpacking strategies? Issue #18583 has been reported by zverok (Victor Shepelev). ---------------------------------------- Feature #18583: Pattern-matching: API for custom unpacking strategies? https://bugs.ruby-lang.org/issues/18583 * Author: zverok (Victor Shepelev) * Status: Open * Priority: Normal ---------------------------------------- I started to think about it when discussing https://github.com/ruby/strscan/pull/30. The thing is, usage of StringScanner for many complicated parsers invokes some kind of branching. In pseudocode, the "ideal API" would allow to write something like this: ```ruby case in /regexp1/ => value_that_matched # use value_that_matched in /regexp2/ => value_that_matched # use value_that_matched # ... ``` This seems "intuitively" that there *should* be some way of implementing it, but we fall short. We can do some StringScanner-specific matcher object which defines its own `#===` and use it with pinning: ```ruby case scanner in ^(Matcher.new(/regexp1/)) => value_that_matched # ... ``` But there is no API to tell how the match result will be unpacked, just the whole `StringScanner` will be put into `value_that_matched`. So, I thought that maybe it would be possible to define some kind of API for pattern-like objects, the method with signature like `try_match_pattern(value)`, which by default is implemented like `return value if self === value`, but can be redefined to return something different, like part of the object, or object transformed somehow. This will open some interesting (if maybe uncanny) possibilities: not just slicing out the necessary part, but something like ```ruby value => ^(type_caster(Integer)) => int_value ``` So... Just a discussion topic! -- https://bugs.ruby-lang.org/ Unsubscribe: