Add adapter that does not preallocate

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

1 files changed, 38 insertions, 0 deletions

diff --git a/src/hashmap.rs b/src/hashmap.rs
index dd95b34..60bc88a 100644
--- a/src/hashmap.rs
+++ b/src/hashmap.rs
@@ -77,6 +77,44 @@ impl<K, V> FromIterator<(K, V)> for CollectOnceHashMap<K, V, std::collections::h
     }
 }
 
+/// See `CollectOnceHashMap`
+pub struct CollectOnceHashMapNoPrealloc<K, V, S = std::collections::hash_map::RandomState>
+    where K: Eq + Hash + Debug
+{
+    inner: std::result::Result<HashMap<K, V, S>, Error<K>>
+}
+
+impl<K, V, S> From<CollectOnceHashMapNoPrealloc<K, V, S>> for CollectOnceHashMap<K, V, S>
+    where K: Eq + Hash + Debug
+{
+    fn from(cohm: CollectOnceHashMapNoPrealloc<K, V, S>) -> Self {
+        CollectOnceHashMap { inner: cohm.inner }
+    }
+}
+
+impl<K, V> FromIterator<(K, V)> for CollectOnceHashMapNoPrealloc<K, V, std::collections::hash_map::RandomState>
+    where K: Eq + Hash + Debug
+{
+    fn from_iter<T>(iter: T) -> Self
+        where T: IntoIterator<Item = (K, V)>
+    {
+        let mut hm = HashMap::new();
+        for (element_key, element_value) in iter.into_iter() {
+            if hm.contains_key(&element_key) {
+                return CollectOnceHashMapNoPrealloc {
+                    inner: Err(Error::DuplicatedKey(element_key))
+                }
+            } else {
+                hm.insert(element_key, element_value);
+            }
+        }
+
+        CollectOnceHashMapNoPrealloc {
+            inner: Ok(hm)
+        }
+    }
+}
+
 
 #[cfg(test)]
 mod tests {