当我们可以选择将变量设为外部时,为什么我们通过引用传递？

The problem with global variables is
that since every function has access
to these,it becomes increasingly hard
to figure out which functions actually
read and write these variables.

To understand how the application
works,you pretty much have to take
into account every function which
modifies the global state. That can be
done,but as the application grows it
will get harder to the point of being
virtually impossible (or at least a
complete waste of time).

If you don’t rely on global variables,you can pass state around between different functions as needed. That way you stand a much better chance of understanding what each function does,as you don’t need to take the global state into account.