Globals (or no more non-intended assignment to this thread) :)

[caseyh@...]

> I still think the main problem is non-intended assignment to  
> globals, which creates hard-to-find bugs.

> The simple policy of requiring a global declaration to assign to  
> globals would force programmers to consider whether they really want  
> a global variable.

> -- Roberto

"Non-intended assignment to globals" has always been the main  
challenge with using global variables (or anything crossing module  
boundaries that can be assigned to).