49 lines
926 B
V
49 lines
926 B
V
interface Widget {
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}
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interface ResizableWidget {
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Widget
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resize(x int, y int) int
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}
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fn draw(w Widget) {
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// w.resize(10, 20) // <- this won't work, since all Widgets may not implement resize()
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// however, we can check if the underlying type of w implements a different interface:
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if w is ResizableWidget {
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assert w is WidgetB
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rw := w as ResizableWidget
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assert rw is WidgetB
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// if so, we can now safely call that extra method
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assert rw.resize(10, 20) == 200
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} else {
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assert w is WidgetA
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}
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}
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fn draw_ref(w &Widget) {
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if w is ResizableWidget {
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rw := w as ResizableWidget
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assert rw.resize(10, 20) == 200
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} else {
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assert false
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}
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}
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// implements Widget, but not ResizableWidget
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struct WidgetA {
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}
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// implements both Widget and ResizableWidget
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struct WidgetB {
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}
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fn (w WidgetB) resize(x int, y int) int {
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return x * y
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}
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fn test_interface_runtime_conversions() {
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draw(WidgetA{})
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draw(WidgetB{})
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}
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