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Bug #9581

closed

`=~` defined on a subclass of `String` is sometimes ignored, and `String#=~` is called instead

Bug #9581: `=~` defined on a subclass of `String` is sometimes ignored, and `String#=~` is called instead

Added by sawa (Tsuyoshi Sawada) over 11 years ago. Updated over 11 years ago.

Status:
Closed
Assignee:
-
Target version:
-
ruby -v:
2.1.0p0
Backport:
1.9.3: UNKNOWN, 2.0.0: UNKNOWN, 2.1: UNKNOWN
[ruby-core:61151]

Description

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

Updated by srawlins (Sam Rawlins) over 11 years ago Actions
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 #1 [ruby-core:61265]

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

Updated by normalperson (Eric Wong) over 11 years ago Actions
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 #2 [ruby-core:61266]

Thanks both, I will commit the following once others have reviewed:
http://bogomips.org/ruby.git/patch?id=fbd3769851f
(git://80x24.org/ruby.git bug9581)

Updated by Anonymous over 11 years ago Actions
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 #3

  • Status changed from Open to Closed
  • % Done changed from 0 to 100

Applied in changeset r45318.

insns.def (opt_regexpmatch2): respect redefined match op

  • insns.def (opt_regexpmatch2): respect redefined match op
    Thanks to Sam Rawlins for the fix.
  • test/ruby/test_string.rb: test based on Tsuyoshi Sawada's report
    [Bug #9581]
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