presto-main/src/main/java/io/prestosql/operator/scalar/JsonToMapCast.java/JsonToMapCast/JsonToMapCast
class JsonToMapCast:    private JsonToMapCast()
    {
        super(OperatorType.CAST,
                ImmutableList.of(
                        castableFromTypeParameter("K", VARCHAR.getTypeSignature()),
                        castableFromTypeParameter("V", JSON.getTypeSignature())),
                ImmutableList.of(),
                mapType(new TypeSignature("K"), new TypeSignature("V")),
                ImmutableList.of(JSON.getTypeSignature()),
                true);
    }