Namespaces like C++

[Andrey via Digitalmars-d-learn]

Hello, can I using namespaces like in C++, for example: 
ui::Widget or ui::Manager? I created ui/widget.d and ui/manager.d 
for implementation classes Widget and Manager, bun I can't import 
their correctly for using ui.Manager uiManager;
If it is impossible, then what is the best way to using 
namespaces in D? Should I naming my classes with prefix e.g. 
UIManager and UIWidget?