Add comment for type

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/hashmap.rs b/src/hashmap.rs
index ebb6321..dd95b34 100644
--- a/src/hashmap.rs
+++ b/src/hashmap.rs
@@ -21,6 +21,14 @@ pub enum Error<K>
     Unknown,
 }
 
+/// An iterator adapter to collect into a HashMap or error if the iterator yields a key twice
+///
+/// # Note
+///
+/// The FromIterator implementation for this type preallocates a hashmap using the
+/// Iterator::size_hint() function for the size of the hashmap.
+///
+/// For an adaptor that does not preallocate, have a look at `CollectOnceHashMapNoPrealloc`.
 pub struct CollectOnceHashMap<K, V, S = std::collections::hash_map::RandomState>
     where K: Eq + Hash + Debug
 {