Implements TryFrom for Deque from array

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Implement `Default` for `CapacityError`.
 - Implement `defmt::Format` for `CapacityError`.
+- Implement `TryFrom` for `Deque` from array.
 
 ## [v0.9.1] - 2025-08-19
 

src/deque.rs

@@ -33,15 +33,15 @@
 //! }
 //! ```
 
+use crate::vec::{OwnedVecStorage, VecStorage, VecStorageInner, ViewVecStorage};
+use crate::CapacityError;
 use core::cmp::Ordering;
 use core::fmt;
 use core::iter::FusedIterator;
 use core::marker::PhantomData;
-use core::mem::MaybeUninit;
+use core::mem::{ManuallyDrop, MaybeUninit};
 use core::{ptr, slice};
 
-use crate::vec::{OwnedVecStorage, VecStorage, VecStorageInner, ViewVecStorage};
-
 /// Base struct for [`Deque`] and [`DequeView`], generic over the [`VecStorage`].
 ///
 /// In most cases you should use [`Deque`] or [`DequeView`] directly. Only use this
@@ -999,11 +999,55 @@ impl<T: PartialEq, const N: usize> PartialEq for Deque<T, N> {
 
 impl<T: Eq, const N: usize> Eq for Deque<T, N> {}
 
+impl<T, const NS: usize, const ND: usize> TryFrom<[T; NS]> for Deque<T, ND> {
+    /// Converts a `[T; NS]` into a `Deque<T, ND>`.
+    ///
+    /// ```
+    /// use heapless::Deque;
+    ///
+    /// let deq1 = Deque::<u8, 5>::try_from([1, 2, 3]).unwrap();
+    /// let mut deq2 = Deque::<u8, 5>::new();
+    /// deq2.push_back(1).unwrap();
+    /// deq2.push_back(2).unwrap();
+    /// deq2.push_back(3).unwrap();
+    ///
+    /// assert_eq!(deq1, deq2);
+    /// ```
+    type Error = (CapacityError, [T; NS]);
+
+    /// Converts a `[T; NS]` array into a `Deque<T, ND>`.
+    ///
+    /// Returns back the `value` if NS > ND.
+    fn try_from(value: [T; NS]) -> Result<Self, Self::Error> {
+        if NS > ND {
+            return Err((CapacityError, value));
+        }
+
+        let mut deq = Self::default();
+        let value = ManuallyDrop::new(value);
+
+        // SAFETY: We already ensured that value fits in deq.
+        unsafe {
+            ptr::copy_nonoverlapping(
+                value.as_ptr(),
+                deq.buffer.buffer.as_mut_ptr().cast::<T>(),
+                NS,
+            );
+        }
+
+        deq.front = 0;
+        deq.back = NS;
+        deq.full = NS == ND;
+
+        Ok(deq)
+    }
+}
+
 #[cfg(test)]
 mod tests {
-    use static_assertions::assert_not_impl_any;
-
     use super::Deque;
+    use crate::CapacityError;
+    use static_assertions::assert_not_impl_any;
 
     // Ensure a `Deque` containing `!Send` values stays `!Send` itself.
     assert_not_impl_any!(Deque<*const (), 4>: Send);
@@ -1545,4 +1589,89 @@ mod tests {
 
         assert_eq!(a, b);
     }
+
+    #[test]
+    fn try_from_array() {
+        // Array is too big error.
+        assert!(matches!(
+            Deque::<u8, 3>::try_from([1, 2, 3, 4]),
+            Err((CapacityError, [1, 2, 3, 4]))
+        ));
+
+        // Array is at limit.
+        let deq1 = Deque::<u8, 3>::try_from([1, 2, 3]).unwrap();
+        let mut deq2 = Deque::<u8, 3>::new();
+        deq2.push_back(1).unwrap();
+        deq2.push_back(2).unwrap();
+        deq2.push_back(3).unwrap();
+        assert!(deq1.is_full());
+        assert_eq!(deq1, deq2);
+
+        // Array is under limit.
+        let deq1 = Deque::<u8, 8>::try_from([1, 2, 3, 4]).unwrap();
+        let mut deq2 = Deque::<u8, 8>::new();
+        deq2.push_back(1).unwrap();
+        deq2.push_back(2).unwrap();
+        deq2.push_back(3).unwrap();
+        deq2.push_back(4).unwrap();
+
+        assert!(!deq1.is_full());
+        assert_eq!(deq1, deq2);
+    }
+
+    #[test]
+    fn try_from_array_with_zst() {
+        #[derive(Debug, PartialEq, Copy, Clone)]
+        struct ZeroSizedType;
+
+        // Test with ZST (zero-sized type)
+        let deq1 =
+            Deque::<ZeroSizedType, 5>::try_from([ZeroSizedType, ZeroSizedType, ZeroSizedType])
+                .unwrap();
+        let mut deq2 = Deque::<ZeroSizedType, 5>::new();
+        deq2.push_back(ZeroSizedType).unwrap();
+        deq2.push_back(ZeroSizedType).unwrap();
+        deq2.push_back(ZeroSizedType).unwrap();
+
+        assert_eq!(deq1, deq2);
+        assert_eq!(deq1.len(), 3);
+    }
+
+    #[test]
+    fn try_from_array_drop() {
+        droppable!();
+
+        // Array is over limit.
+        {
+            let _result = Deque::<Droppable, 2>::try_from([
+                Droppable::new(),
+                Droppable::new(),
+                Droppable::new(),
+            ]);
+        }
+
+        assert_eq!(Droppable::count(), 0);
+
+        // Array is at limit.
+        {
+            let _result = Deque::<Droppable, 3>::try_from([
+                Droppable::new(),
+                Droppable::new(),
+                Droppable::new(),
+            ]);
+        }
+
+        assert_eq!(Droppable::count(), 0);
+
+        // Array is under limit.
+        {
+            let _result = Deque::<Droppable, 4>::try_from([
+                Droppable::new(),
+                Droppable::new(),
+                Droppable::new(),
+            ]);
+        }
+
+        assert_eq!(Droppable::count(), 0);
+    }
 }