Document UpState
#[cfg(feature = "frunk")]
use frunk::{from_generic, generic::Generic, hlist::HAppender, into_generic};
+/// Constructs a structure from another structure and a field.
+///
+/// Let `X` be a structure of `field1, ..., fieldN`, `Y` be `field1, ...,
+/// fieldN, fieldN+1`. Both `X` and `Y` implement [`Generic`]. Then `Y::up(x,
+/// fieldN+1)` constructs `Y` from all the fields of `x: X` plus `Y`'s
+/// `fieldN+1`.
+///
+/// [`Generic`]: https://docs.rs/frunk/latest/frunk/generic/trait.Generic.html
#[cfg(feature = "frunk")]
pub trait UpState: Sized {
fn up<T1, T1Repr, F>(src: T1, field: F) -> Self
