Macro user_type_convert_to_writeable 

macro_rules! user_type_convert_to_writeable {
    (VarInt, $e:expr) => { ... };
    (VarIntPrefixedVec <$inner:ident>, $e:expr) => { ... };
    (ShortPrefixedVec <$inner:ident>, $e:expr) => { ... };
    (LengthInferredVecU8, $e:expr) => { ... };
    (Angle, $e:expr) => { ... };
    ($typ:ty, $e:expr) => { ... };
}