[ruby-talk:7967] Re: defined? problem?

Dave Thomas <[e-mail]> 
wrote:
>David Alan Black <[e-mail]> writes:
>
>> The behavior I find most surprising -- even given the underlying
>> principle of defining a variable upon seeing an assignment to it -- is
>> illustrated by this:
>> 
>>    irb(main):003:0> if m then m = 123 end
>>    NameError: undefined local variable or method `m' for #<Object:0x4017fc90>
>>    (irb):3:in `irb_binding'
>>    irb(main):004:0> if m then m = 123 end
>>    nil
>
>Let's play Ruby during the parsing stage (remember, we're not
>executing code at this point)
>
>   if                        <keyword, I'm looking for some
>                              kind of expression>
>      m                      <name. I haven't seen an assignment,
>                              so it's a method call>
>        then                 <keyword>
>             m = 123         <assignment to m. remember the fact that
>                              m is a variable for future reference> 

Hold it right there. Is it really valid to 
"remember the fact that m is a variable"? It 
seems like that decision should be held off until 
runtime.

Consider code like this:
======================
if true
	def a
		"method a"
	end
end

if true
	b = 6
	def c
		"method c"
	end
else
	def b
		"method b"
	end
	c = 6
end

if true
	def d
		"method d"
	end
	e = 6
else
	d = 6
	def e
		"method e"
	end
end


puts a
puts b
puts c
puts d
puts e
=================

What result would you expect? In reality, a is a 
method, b and e are 6, and c and d are nil.

It probably makes perfect sense if you know how 
interpreters work. From the outside, it is a 
surprise to me.

Kevin