So I get your point, but to this reasonably-Ruby-familiar human, this is not surprising. `name=` is the name of the setter method that you'd need to have here if you were to set the field; it doesn't exist, so Ruby's telling you so. It's a pretty common idiom.

It could be improved--not easily; a setter method does not necessarily have to map to a data type, and Ruby itself doesn't know what you mean here because the Data type is in the stdlib but doesn't appear to be a compiler special case--but this is a bit nitpicking, and I would perhaps gently push back on changing the error message because it's representing what you really do need to know in Ruby once you're past the level one "driving Rails" usage of Ruby. Getting an error message other than this one would obfuscate what's happening and leave me as a long-time Ruby user pretty confused.