Why does map_res closure not simply return Option
gdennie opened this issue · 3 comments
In nom (currently v7.1.3 with rust nightly)...
The map_res function requires a closure that returns core::result::Result<T,E>. However, map_res does actually use the Err discriminant's value. However, requiring a Result<T,E> result type complicates type conformance as well as the code. As such, I am curious as to why Option<T> was not chosen for the closure result type.
map_res requires its error value to implement nom::err::FromExternalError which requires the result error value. However, current error type implementations by nom namely (), (I, ErrorKind), and VerboseError do not even hold this value.
It is meant for use with a custom error type that can hold the external error yes. If you don't use it, why not try map_opt?
Did not know about map_opt, as such. Recall seeing the name once or twice in the docs. Will now be using it.
Thanks.