Data members on local Slice exceptions and structs are mapped to Swift stored properties, just like data members on non-local Slice types are mapped to stored properties on the corresponding struct or exception class.
Data members on local Slice classes are mapped to computed properties (with both get and set) on the corresponding Swift protocol.
A local Slice type can have a data member of type local interface or class: it is mapped as a Swift property with the mapped Swift protocol as its type. Such property can have a null value unless you define it using the
["swift:nonnull"] metadata directive.