print_display: Comment at end indicates an error, yet example compiles and runs without error.

[systemdlete]

As a learner, I was confused by the way this comment was written. Certainly, the absence of the binary method (trait?) will cause an error, but the example does not actually attempt to do so (for an obvious reason).

When I read "Error." I thought, ok, there is an error. But where? Reading further on, this is revealed, of course, for the particular choice (why that particular one?) of demonstrating the absence of the binary implementation. Maybe rewording this section would be helpful. In particular, maybe leave out the sentence fragment ("Error.").

"This will not work" should probably be preceded by a line break, and reworded to "The following will not work:" or something like that. It seems all run-together as it stands.

I am sure that if I come back to this example in the future, I might grin at how "obvious" this all seems. But at this early point in my own learning, it throws me off a bit. (Case in point; After just a few days, coming back to it and reviewing it for the purposes of posting this issue, it already makes more sense to me.)