It is possible to attempt use a variable more than once.
The Swift example was caused by shadowing. There was a global print() function and a instance print() method (taking one parameter, sender: AnyObject). If you called print() in a class not descending from NSView it printed the string in the console as expected. But if you called it in a class descending from NSView you got a print dialog as the instance method shadowed the global function. They fixed the issue long ago of course.
The Swift example was caused by shadowing. There was a global print() function and a instance print() method (taking one parameter, sender: AnyObject). If you called print() in a class not descending from NSView it printed the string in the console as expected. But if you called it in a class descending from NSView you got a print dialog as the instance method shadowed the global function. They fixed the issue long ago of course.