Bug #9581
closed`=~` defined on a subclass of `String` is sometimes ignored, and `String#=~` is called instead
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 10 years ago
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 thatRB_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 10 years ago
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 10 years ago
- 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]