From: Thomas Wieczorek <wieczo.yo@...>
Date: 2008-01-23T06:05:12+09:00
Subject: Re: why must I initialize this variable?

Hello!

On Jan 22, 2008 6:40 PM, matt neuburg <matt@tidbits.com> wrote:
> Here's a simple variable initialization / scope question. In the
> following code:
>

First of all I think that you confuse assignment(=) with
comparison(==). Every operation in Ruby returns a value.
In assignment the right hand side is returned
> irb
h = {:test => "cool"}
#returns {:test => "cool"}

In comparison, either true or false are returned. An assignment
returns true if you don't assign _nil_ or _false_.
> irb
if foo = "bar"
   puts foo
end
(irb):16: warning: found = in conditional, should be ==
As you see, irb or running Ruby with the '-w' will give you a warning,
that you used an assignment in a

> h = {:test => "cool"}
> k = :test
> result = nil
> puts "#{result}" if (result = h[k])
>

I am not sure if I am right: Here it tried to get the value of result
first, if it doesn't exist, an exception occurs. After looking up
result, it tests the if-clause.

> ...if I omit the third line (initializing "result"), I get an error.
> Why? Intuitively I would have expected the second part of the 4th line
> to create / initialize "result".
>
> Another way of understanding my confusion is to notice that this *does*
> work:
>
> h = {:test => "cool"}
> k = :test
> if (result = h[k]) then puts "#{result}" end
>

Here, you assign, the assignment returns "cool", which is true and
then you print out the existing variable.

I hope you understand  what I mean.

Regards,
Thomas