From b255dfaf611f492f18a6c76ce6562bf0649273bb Mon Sep 17 00:00:00 2001
From: Temirkhan Myrzamadi <hirrolot@gmail.com>
Date: Sun, 26 Jul 2020 04:43:08 +0600
Subject: [PATCH] Document UpState

---
 src/up_state.rs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/up_state.rs b/src/up_state.rs
index 698e32ab..67b3e43e 100644
--- a/src/up_state.rs
+++ b/src/up_state.rs
@@ -1,6 +1,14 @@
 #[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