Added TinyVec::with_initial_len() function and associated tests. (#224)

Author: lordmulder

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## Next (Unreleased)
+
+* Adds `TinyVec::with_initial_len`
+
 ## 1.12
 
 * Add `schemars` support.

src/tinyvec.rs

@@ -684,6 +684,33 @@ impl<A: Array> TinyVec<A> {
     }
   }
 
+  /// Makes a default-initialized TinyVec with the given initial length.
+  ///
+  /// If the requested length is less than or equal to the array capacity you
+  /// get an inline vec. If it's greater than you get a heap vec.
+  /// ```
+  /// # use tinyvec::*;
+  /// let t = TinyVec::<[u8; 10]>::with_initial_len(5);
+  /// assert!(t.is_inline());
+  /// assert_eq!(t.len(), 5);
+  ///
+  /// let t = TinyVec::<[u8; 10]>::with_initial_len(20);
+  /// assert!(t.is_heap());
+  /// assert_eq!(t.len(), 20);
+  /// ```
+  #[inline]
+  #[must_use]
+  pub fn with_initial_len(len: usize) -> Self
+  where
+    A::Item: Clone,
+  {
+    if len <= A::CAPACITY {
+      TinyVec::Inline(ArrayVec::from_array_len(A::default(), len))
+    } else {
+      TinyVec::Heap(vec![A::Item::default(); len])
+    }
+  }
+
   /// Converts a `TinyVec<[T; N]>` into a `Box<[T]>`.
   ///
   /// - For `TinyVec::Heap(Vec<T>)`, it takes the `Vec<T>` and converts it into

tests/tinyvec.rs

@@ -33,6 +33,22 @@ fn TinyVec_capacity() {
   tv.move_to_the_heap();
   tv.extend_from_slice(&[1, 2, 3, 4]);
   assert_eq!(tv.capacity(), 4);
+
+  let tv = TinyVec::<[i32; 10]>::with_capacity(5);
+  assert!(tv.is_inline());
+  assert!(tv.capacity() >= 5);
+
+  let tv = TinyVec::<[i32; 10]>::with_capacity(20);
+  assert!(tv.is_heap());
+  assert!(tv.capacity() >= 20);
+
+  let tv = TinyVec::<[i32; 10]>::with_initial_len(5);
+  assert!(tv.is_inline());
+  assert_eq!(tv.len(), 5);
+
+  let tv = TinyVec::<[i32; 10]>::with_initial_len(20);
+  assert!(tv.is_heap());
+  assert_eq!(tv.len(), 20);
 }
 
 #[test]