Hands-On Design Patterns and Best Practices with Julia

Typed arguments

We know that our implementation of the move functions comes with some implicit design assumptions:

• The value of v should be a numerical value, as implied by the + or - operator.
• The widget has to be a Widget object, or at least something that contains a Position object, as implied by the access of the position field.

For these reasons, it's generally safer to define functions with some type information. Having said that, the move_up! function can be redefined as follows:

move_up!(widget::Widget, v::Int) = widget.position.y -= v

If we just define all move functions the same way, then debugging becomes easier. Suppose that we make the same mistake as we did in the preceding code by passing an integer as the first argument: ...