Error code E0193
Note: this error code is no longer emitted by the compiler.
where
clauses must use generic type parameters: it does not make sense to use
them otherwise. An example causing this error:
This use of a where
clause is strange - a more common usage would look
something like the following:
Here, we're saying that the implementation exists on Wrapper only when the
wrapped type T
implements Clone
. The where
clause is important because
some types will not implement Clone
, and thus will not get this method.
In our erroneous example, however, we're referencing a single concrete type.
Since we know for certain that Wrapper<u32>
implements Clone
, there's no
reason to also specify it in a where
clause.