code: public Implementation.Composable withAssigner(Assigner assigner) {
          return new MethodDelegation(implementationDelegate,
                  parameterBinders,
                  ambiguityResolver,
                  terminationHandler,
                  bindingResolver,
                  assigner);
      }
docs: Applies an assigner to the method delegation that is used for assigning method return and parameter types.
  
  @param assigner The assigner to apply.
  @return A method delegation implementation that makes use of the given designer.