Motive behind !empty() with front() instead of Optional front()

[Per Nordlöw]

On Friday, 26 March 2021 at 15:02:27 UTC, Nick Treleaven wrote:
> compile-time checked optional types is that the value has to 
> exist in order to unwrap the optional.

Can you elaborate on what you mean by "compile-time checked 
optional types"?