Function has_codec 

pub const fn has_codec(kind: &TypeKind) -> bool

Whether rust_codec gives a type of this kind a codec of its own: an aggregate (structure, union, valuetype), an enumeration, a bitmask or a bitset. A bitmask’s answer is empty, since its Rust form is an alias of a primitive and its member site writes the holder. Every other kind — a primitive, a string, a collection, an alias — is written where it is used and has no impl to hang a pair on.