TryPush trait to enable non-reallocating pushes

src/impls/index.rs

@@ -248,7 +248,11 @@ where
     /// Reserve space for `additional` elements.
     #[inline]
     pub fn reserve(&mut self, additional: usize) {
-        self.smol.reserve(additional);
+        if self.chonk.is_empty() {
+            self.smol.reserve(additional);
+        } else {
+            self.chonk.reserve(additional);
+        }
     }
 
     /// Remove all elements.
@@ -299,6 +303,15 @@ where
     fn is_empty(&self) -> bool {
         self.is_empty()
     }
+
+    #[inline]
+    fn capacity(&self) -> usize {
+        if self.chonk.is_empty() {
+            self.smol.capacity()
+        } else {
+            self.chonk.capacity()
+        }
+    }
 }
 
 impl<S, L> IndexContainer<usize> for IndexList<S, L>
@@ -407,6 +420,16 @@ where
     fn heap_size<F: FnMut(usize, usize)>(&self, callback: F) {
         self.spilled.heap_size(callback);
     }
+
+    #[inline]
+    fn capacity(&self) -> usize {
+        if self.spilled.is_empty() {
+            // TODO: What else could we do here? `usize::MAX`?
+            1
+        } else {
+            self.spilled.capacity()
+        }
+    }
 }
 
 impl<S, L> IndexContainer<usize> for IndexOptimized<S, L>
@@ -439,8 +462,25 @@ where
     where
         I::IntoIter: ExactSizeIterator,
     {
-        for item in iter {
-            self.push(item);
+        let mut iter = iter.into_iter();
+        if !self.spilled.is_empty() {
+            // We certainly push into `spilled`, so reserve enough space.
+            let (lower, upper) = iter.size_hint();
+            self.spilled.reserve(upper.unwrap_or(lower));
+        }
+        while let Some(item) = iter.next() {
+            if self.spilled.is_empty() {
+                let inserted = self.strided.push(item);
+                if !inserted {
+                    // This is a transition point from pushing into `strided` to pushing into
+                    // `spilled`.
+                    let (lower, upper) = iter.size_hint();
+                    self.spilled.reserve(upper.unwrap_or(lower));
+                    self.spilled.push(item);
+                }
+            } else {
+                self.spilled.push(item);
+            }
         }
     }
 

src/impls/mirror.rs

@@ -6,7 +6,9 @@ use std::marker::PhantomData;
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
 
-use crate::{Index, IntoOwned, Push, Region, RegionPreference, ReserveItems};
+use crate::{
+    CanPush, Index, IntoOwned, Push, Region, RegionPreference, Reserve, ReserveItems, TryPush,
+};
 
 /// A region for types where the read item type is equal to the index type.
 ///
@@ -99,6 +101,25 @@ where
     }
 }
 
+impl<T> TryPush<T> for MirrorRegion<T>
+where
+    for<'a> T: Index + IntoOwned<'a, Owned = T>,
+{
+    #[inline(always)]
+    fn try_push(&mut self, item: T) -> Result<Self::Index, T> {
+        Ok(item)
+    }
+}
+
+impl<T> CanPush<T> for MirrorRegion<T> {
+    fn can_push<I>(&self, _: I) -> bool
+    where
+        I: Iterator<Item = T> + Clone,
+    {
+        true
+    }
+}
+
 impl<T> Push<&T> for MirrorRegion<T>
 where
     for<'a> T: Index + IntoOwned<'a, Owned = T>,
@@ -109,6 +130,25 @@ where
     }
 }
 
+impl<'a, T> CanPush<&'a T> for MirrorRegion<T> {
+    fn can_push<I>(&self, _: I) -> bool
+    where
+        I: Iterator<Item = &'a T> + Clone,
+    {
+        true
+    }
+}
+
+impl<'b, T> TryPush<&'b T> for MirrorRegion<T>
+where
+    for<'a> T: Index + IntoOwned<'a, Owned = T>,
+{
+    #[inline(always)]
+    fn try_push(&mut self, item: &'b T) -> Result<Self::Index, &'b T> {
+        Ok(*item)
+    }
+}
+
 impl<T> Push<&&T> for MirrorRegion<T>
 where
     for<'a> T: Index + IntoOwned<'a, Owned = T>,
@@ -119,6 +159,16 @@ where
     }
 }
 
+impl<'b, 'c, T> TryPush<&'b &'c T> for MirrorRegion<T>
+where
+    for<'a> T: Index + IntoOwned<'a, Owned = T>,
+{
+    #[inline(always)]
+    fn try_push(&mut self, item: &'b &'c T) -> Result<Self::Index, &'b &'c T> {
+        Ok(**item)
+    }
+}
+
 impl<T> ReserveItems<T> for MirrorRegion<T>
 where
     for<'a> T: Index + IntoOwned<'a, Owned = T>,
@@ -145,6 +195,14 @@ where
     }
 }
 
+impl<T> Reserve for MirrorRegion<T> {
+    type Reserve = ();
+
+    fn reserve(&mut self, (): &Self::Reserve) {
+        // No storage
+    }
+}
+
 macro_rules! implement_for {
     ($index_type:ty) => {
         impl RegionPreference for $index_type {

src/impls/option.rs

@@ -3,7 +3,7 @@
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
 
-use crate::{IntoOwned, Push, Region, RegionPreference, ReserveItems};
+use crate::{IntoOwned, Push, Region, RegionPreference, Reserve, ReserveItems};
 
 impl<T: RegionPreference> RegionPreference for Option<T> {
     type Owned = Option<T::Owned>;
@@ -167,6 +167,17 @@ where
     }
 }
 
+impl<R> Reserve for OptionRegion<R>
+where
+    R: Reserve,
+{
+    type Reserve = R::Reserve;
+
+    fn reserve(&mut self, size: &Self::Reserve) {
+        self.inner.reserve(size);
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use crate::{MirrorRegion, OwnedRegion, Region, ReserveItems};

src/impls/result.rs

@@ -3,7 +3,7 @@
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
 
-use crate::{IntoOwned, Push, Region, RegionPreference, ReserveItems};
+use crate::{IntoOwned, Push, Region, RegionPreference, Reserve, ReserveItems};
 
 impl<T: RegionPreference, E: RegionPreference> RegionPreference for Result<T, E> {
     type Owned = Result<T::Owned, E::Owned>;
@@ -194,6 +194,19 @@ where
     }
 }
 
+impl<T, E> Reserve for ResultRegion<T, E>
+where
+    T: Reserve,
+    E: Reserve,
+{
+    type Reserve = (T::Reserve, E::Reserve);
+
+    fn reserve(&mut self, (t, e): &Self::Reserve) {
+        self.oks.reserve(t);
+        self.errs.reserve(e);
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use crate::{MirrorRegion, OwnedRegion, Region, ReserveItems};