From: matz@... Date: 2019-11-28T04:25:42+00:00 Subject: [ruby-core:96006] [Ruby master Feature#16355] Raise NoMatchingPatternError when `expr in pat` doesn't match Issue #16355 has been updated by matz (Yukihiro Matsumoto). I accept this proposal for two reasons: * as OP described, returning boolean values from `in` pattern matching masks match failure. This can cause serious problems. * By this change, we cannot use `in` pattern matching in `if` conditionals. But this style can be easily expressed by `case` pattern matching. Matz. ---------------------------------------- Feature #16355: Raise NoMatchingPatternError when `expr in pat` doesn't match https://bugs.ruby-lang.org/issues/16355#change-82842 * Author: ktsj (Kazuki Tsujimoto) * Status: Open * Priority: Normal * Assignee: * Target version: ---------------------------------------- Currently, single line pattern matching(`expr in pat`) returns true or false. ``` [1, 2, 3] in [x, y, z] #=> true (with assigning 1 to x, 2 to y, and 3 to z) [1, 2, 3] in [1, 2, 4] #=> false ``` I think `expr in pat` should raise an exception when it doesn't match. Because if a user doesn't check the return value of `expr in pat`, matching failure occurs implicitly and it may cause problems in subsequent processes. ``` expr in [0, x] # A user expects it always matches, but if it doesn't match... ... (snip) ... x.foo #=> NoMethodError (undefined method `foo' for nil:NilClass) ``` I also propose that `expr in pat` returns the result of `expr` if it matches. It is similar to assignment. ``` x, y, z = 1, 2, 3 #=> [1, 2, 3] [1, 2, 3] in [x, y, z] #=> [1, 2, 3] ``` ---Files-------------------------------- expr-in-pat-raises-error.patch (2.59 KB) -- https://bugs.ruby-lang.org/ Unsubscribe: