From: sam.rawlins@... Date: 2014-03-03T20:28:11+00:00 Subject: [ruby-core:61265] [ruby-trunk - Bug #9581] `=~` defined on a subclass of `String` is sometimes ignored, and `String#=~` is called instead Issue #9581 has been updated by Sam Rawlins. Three functions relate directly to this bug: * match_op_gen() in parse.y [1], which compiles two expressions separated by a `=~` into some kind of MATCH node. When it sees that the right side is a literal Regexp, it returns a NODE_MATCH3 node. * iseq_compile_each() in compile.c [2], which upon seeing NODE_MATCH3 _flips_ the receiver and the value. Then, if the InstructionSequence option `specialized_instruction` is true [3] (which it is, by default), the code falls to line 4804, which creates an instruction for: * opt_regexpmatch2(), in insns.def [4]. In this function, we optimize the instruction to just `rb_reg_match(obj1,obj2)` after finding that `RB_TYPE_P(obj2, T_STRING)`. Ah ha! The solution is a different test to answer "is obj2 a String?": diff --git a/insns.def b/insns.def index 7942804..7ef4c4c 100644 --- a/insns.def +++ b/insns.def @@ -2154,7 +2154,7 @@ opt_regexpmatch2 (VALUE obj2, VALUE obj1) (VALUE val) { - if (RB_TYPE_P(obj2, T_STRING) && + if (CLASS_OF(obj2) == rb_cString && BASIC_OP_UNREDEFINED_P(BOP_MATCH, STRING_REDEFINED_OP_FLAG)) { val = rb_reg_match(obj1, obj2); } I don't think this represents a great slowdown. [1] http://svn.ruby-lang.org/cgi-bin/viewvc.cgi/trunk/parse.y?view=markup#l8535 [2] http://svn.ruby-lang.org/cgi-bin/viewvc.cgi/trunk/compile.c?view=markup#l4770 [3] The bug can be temporarily remedied with today's Ruby using: RubyVM::InstructionSequence.compile_option = { specialized_instruction: false } s =~ /abc/ #=> :foo [4] http://svn.ruby-lang.org/cgi-bin/viewvc.cgi/trunk/insns.def?view=markup#l2151 ---------------------------------------- Bug #9581: `=~` defined on a subclass of `String` is sometimes ignored, and `String#=~` is called instead https://bugs.ruby-lang.org/issues/9581#change-45603 * Author: Tsuyoshi Sawada * Status: Open * Priority: Normal * Assignee: * Category: * Target version: * ruby -v: 2.1.0p0 * Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN, 2.1: UNKNOWN ---------------------------------------- As is reported on StackOverflow (http://stackoverflow.com/questions/22103018) by Gabriel, overridden `=~` on a subclass of `String` is sometimes ignored, and the original `String#=~` is called. Particularly, when we have: class MyString < String def =~ re; :foo end end s = MyString.new("abc") these give the correct result: r = /abc/; s =~ r # => :foo s.send(:=~, r) # => :foo s.send(:=~, /abc/) # => :foo but in this case, `MyString#=~` is ignored, and `String#=~` is called instead: s =~ /abc/ # => 0 -- http://bugs.ruby-lang.org/