Error code E0393
A type parameter which references Self
in its default value was not specified.
Erroneous code example:
ⓘ
A trait object is defined over a single, fully-defined trait. With a regular
default parameter, this parameter can just be instantiated in. However, if the
default parameter is Self
, the trait changes for each concrete type; i.e.
i32
will be expected to implement A<i32>
, bool
will be expected to
implement A<bool>
, etc... These types will not share an implementation of a
fully-defined trait; instead they share implementations of a trait with
different parameters instantiated in for each implementation. This is
irreconcilable with what we need to make a trait object work, and is thus
disallowed. Making the trait concrete by explicitly specifying the value of the
defaulted parameter will fix this issue. Fixed example: