How to avoid global variables

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Global variables should be avoided because they inhibit code reuse. Multiple widgets/applications can nicely live within the same main loop. This allows you to abstract what you now think of as a single GUI into a library that creates such GUI on request, so that (for instance) a single launcher can launch multiple top-level GUIs sharing the same process.

If you use global variables, this is impossible because multiple GUI instances will trump each other’s state.

The alternative to global variables is to associate the needed attributes with a top-level widget, and to create sub-widgets that point to the same top-level widgets. Then, for example, a menu action will use its top-level widget to reach the currently opened file in order to operate on it.

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