Extrange String#=~ behaviour

[Iñaki Baz Castillo]

Hi, I can't understand it:

class String
def =3D~ obj
puts "Sorry, I don't compare"
end
end


a) OK
irb> "string" =3D~ 1234
Sorry, I don't compare
nil

b) =C2=BF?
irb> "string" =3D~ /string/
0

c) OK
irb> "string".send"=3D~", 1234)
Sorry, I don't compare
nil

d) OK
irb> "string".send"=3D~", /string/)
Sorry, I don't compare
nil


Could I know why case "b" perform the normal regexp comparission instead of=
=20
invoking the re-defined String#=3D~ method??

Thanks.


=2D-=20
I=C3=B1aki Baz Castillo

 

[Iñaki Baz Castillo]

Sorry, the subject must be "Strange"



=2D-=20
I=C3=B1aki Baz Castillo

 

[7stud --]

Hi, I can't understand it:

class String
def =~ obj
puts "Sorry, I don't compare"
end
end

b) ¿?
irb> "string" =~ /string/
0

Could I know why case "b" perform the normal regexp comparission instead
of
invoking the re-defined String#=~ method??

To me that suggests that String#=~ calls Regexp#=~. However, I am
having no luck proving that. I can't even override Regexp#=~:

class Regexp
def =~(obj)
puts "goodbye"
end
end

puts /string/ =~ "string" #0

 

[lasitha]

Turns out using Regexp.new behaves as expected:

07> "string" =3D~ Regexp.new('string')
Sorry, I don't compare
--> nil

class Regexp
=A0def =3D~(obj)
=A0 =A0puts "goodbye"
=A0end
end

puts /string/ =3D~ "string" =A0#0

In this case too:

08> Regexp.new('string') =3D~ "string"
goodbye
--> nil

Ruby 1.9 rdoc for Regexp#=3D~ hints at special treatment for regexp literal=
s [1]:
"This assignment is implemented in the Ruby parser. So a regexp
literal is required for the assignment. The assignment is not occur if
the regexp is not a literal."
But that is in the context of assigning to ?<var> type named captures
within a regexp on the LHS, so i don't know if it's relevant.

Hope someone who knows the implementation can shed more light.

Cheers,
lasitha.

[1] http://ruby-doc.org/core-1.9/classes/Regexp.html#M001214

 

[Brian Candler]

Could I know why case "b" perform the normal regexp comparission instead
of
invoking the re-defined String#=~ method??

ParseTree gem may help you.

$ cat strange.rb
class String
def =~ obj
puts "Sorry, I don't compare"
end
end

r1 = "string" =~ 1234
r2 = "string" =~ /string/
r3 = "string".send"=~", 1234)
r4 = "string".send"=~", /string/)

$ parse_tree_show strange.rb
sblock,
sclass,
:String,
nil,
sscope,
sdefn,
:=~,
sscope,
sblock,
sargs, bj),
sfcall, uts, sarray, sstr, "Sorry, I don't
compare")))))))),
slasgn, :r1, scall, sstr, "string"), :=~, sarray, slit,
1234)))),
slasgn, :r2, smatch3, slit, /string/), sstr, "string"))),
slasgn,
:r3,
scall, sstr, "string"), :send, sarray, slit, :=~), slit,
1234)))),
slasgn,
:r4,
scall,
sstr, "string"),
:send,
sarray, slit, :=~), slit, /string/)))))
$

You can see that your case (b) is parsed differently as a :match3,
bypassing the normal method dispatch call)

 

[Iñaki Baz Castillo]

You can see that your case (b) is parsed differently as a :match3,
bypassing the normal method dispatch call)

Interesting, thanks a lot.


--=20
I=C3=B1aki Baz Castillo
<[email protected]>