The Metro runtime provides support for:

• a component derived declaration of internal structure and access interfaces
• container support for the establishment and association of internal parts with a component

Declaration of the stuctural presumptions of a component is achieved though a Parts interface exposed as a constructor parameter. A Parts interface is recognized using either the default inner class pattern, or via the assertion of part-semanitcs using the parts annotation. The following code fragment demonstrates a component that declares its internal structure via an internal Parts inner interface and the usage of that interface as a constructor parameter.

public class Container
{
    public interface Parts
    {
        Widget getWidget();
        Gizmo[] getGizmos();
    }
    
    public Container( final Parts parts )
    {
        Widget widget = parts.getWidget();
        Gizmo[] gizmos = parts.getGizmos();
        
        ...
        
    }
    
    ...
}