Alex Gutteridge
1/29/2007 6:48:00 AM
On Mon, 2007-01-29 at 14:41 +0900, Nasir Khan wrote:
> Please look at this snippet -
>
> --------------------------------
> class Test
>
> def initialize
> @hash = {}
> end
>
> def method_missing(m,*a)
> if m.to_s =~ /=$/
> Test.class_eval do
> define_method($`.to_sym) do #accessor
> @hash[$`.to_sym]
> end
> define_method(m) do |arg| #mutator
> @hash[$`.to_sym] = arg.split(",")
> end
> end
> send m, *a
> else
> raise NoMethodError, "#{m}"
> end
> end
> end
>
> t = Test.new
> t.a = "hello"
> puts t.a
>
[snip]
> First of all can anyone please explain why it runs with debugger while fails
> with normal interpreter?
>
> Second what is wrong with the snippet?
Perhaps you already know this, but using a local variable in place of $`
fixes your code:
class Test
def initialize
@hash = {}
end
def method_missing(m,*a)
if m.to_s =~ /=$/
key = $` #added here
Test.class_eval do
define_method(key.to_sym) do #accessor
@hash[key.to_sym]
end
define_method(m) do |arg| #mutator
@hash[key.to_sym] = arg.split(",")
end
end
send m, *a
else
raise NoMethodError, "#{m}"
end
end
end
t = Test.new
t.a = "hello,world"
puts t.a
$` is getting clobbered when you go into Test.class_eval so it gets set
to nil. Why this is different to a local variable I'm not sure to be
honest (ditto for why debug mode should be different).
As a related, follow up question, can someone explain the difference
between the two class_evals in the following snippet (one works, the
other doesn't):
"foo".match(/oo/)
class Test
end
Test.class_eval do
define_method($`.to_sym) do
puts $` + "oobared"
end
end
Test.new.f
class Test
class_eval do
define_method($`.to_sym) do
puts $` + "oobared"
end
end
end
--
Alex Gutteridge
Kyoto University