private ImmutableList<TypeMirror> resolvedTypeParameters(
        TypeMirror propertyType, String interfaceName) {
      return elements.getTypeElement(interfaceName).getTypeParameters().stream()
          .map(p -> types.asMemberOf(MoreTypes.asDeclared(propertyType), p))
          .collect(toImmutableList());
    }
Parameter object to simplify the branches of {@link #format(CodeBlock, CodeBlock,
TypeMirror)} that call a delegate method.
value/src/main/java/com/google/auto/value/extension/toprettystring/processor/ToPrettyStringExtension.java