[ruby-talk:11610] Re: TkScale variable option can't be an object attribute

R. Mark Volkmann <[e-mail]> wrote:
>Setting the "variable" option of a TkScale is supposed to make it get its
>value from that variable reference.  It seems that this doesn't work if an 
>object attribute used.  Simply changing the "variable" option to refer to 
>a local variable makes it work.  Can anyone confirm whether this is a known 
>bug in the Ruby wrapping of TkScale?

Sorry for replying to this a month later -- nobody else did, and I was
perusing this part of the newsgroup today. =)

You can't use a member variable in the initialization block of a TkScale
simply because it's out of scope.  In the initialization block of a TkScale,
the TkScale object is "self" and so its members (if any) are in scope;
refering to the member variables of another object won't get you far.

This is why you notice that it works when you use a local variable reference
to the object.  As you have probably learned, in ruby, there is a distinction
between your objects and the variable names by which you refer to them.
So when you do the following:

		@member = foo.new
		local = @member

In many OOP languages, like C++, 'local' and 'member' would point to two 
seperate objects (via a copy constructor), but in ruby, both 'local' and 
'member' point to the *same* instance of the 'foo' object!

So ultimately, to bind a TkVariable via the 'variable' directive, you will
have to have a local variable reference to the TkVariable.

Jeremy