Module blog::daily_rfcs::trait_sys::_0255_object_safety

Restrict which traits can be used to make trait objects

Note

Object-safe method

1. require Self : Sized; OR
2. meet all of the following conditions:
   • must not have any type parameters; AND
   • must have a receiver that has type Self or which dereferences to the Self type;
     • for now, this means self, &self, &mut self, or self: Box<Self>, but eventually this should be extended to custom types like self: Rc and so forth.
   • must not use Self (in the future, where we allow arbitrary types for the receiver, Self may only be used for the type of the receiver and only where we allow Sized? types).

Object-safe trait

• all of its methos are object safe.
• the trait does not require that Self : Sized

How to bypass object-safety rules

• split trait into object-safe and non-object-safe parts.
• add where Self: Sized to non-object-safe methods.(derive from Object-safe method rule 1)

RFC: 0255-object-safety