Implement TryFrom<Vec<T>> for ArrayVec<T, N>

src/arrayvec.rs

@@ -772,6 +772,32 @@ impl<T, const CAP: usize> std::convert::TryFrom<&[T]> for ArrayVec<T, CAP>
 }
 
 
+/// Try to create an `ArrayVec` from a vector. This will return an error if the slice was too big to
+/// fit.
+///
+/// ```
+/// use arrayvec::ArrayVec;
+/// use std::convert::TryInto as _;
+///
+/// let array: ArrayVec<_, 4> = vec![1, 2, 3].try_into().unwrap();
+/// assert_eq!(array.len(), 3);
+/// assert_eq!(array.capacity(), 4);
+/// ```
+impl<T, const CAP: usize> std::convert::TryFrom<crate::Vec<T>> for ArrayVec<T, CAP> {
+    type Error = CapacityError;
+
+    fn try_from(vec: crate::Vec<T>) -> Result<Self, Self::Error> {
+        if Self::CAPACITY < vec.len() {
+            Err(CapacityError::new(()))
+        } else {
+            let mut array = Self::new();
+            // SAFETY: Vector length has already been checked
+            unsafe { array.extend_from_iter::<_, false>(vec); }
+            Ok(array)
+        }
+    }
+}
+
 /// Iterate the `ArrayVec` with references to each element.
 ///
 /// ```

src/lib.rs

@@ -18,12 +18,20 @@
 #![doc(html_root_url="https://docs.rs/arrayvec/0.7/")]
 #![cfg_attr(not(feature="std"), no_std)]
 
+#[cfg(not(feature="std"))]
+extern crate alloc;
+
 #[cfg(feature="serde")]
 extern crate serde;
 
 #[cfg(not(feature="std"))]
 extern crate core as std;
 
+#[cfg(feature="std")]
+pub use std::vec::Vec as Vec;
+#[cfg(not(feature="std"))]
+pub use alloc::vec::Vec as Vec;
+
 pub(crate) type LenUint = u32;
 
 macro_rules! assert_capacity_limit {

tests/tests.rs

@@ -6,9 +6,6 @@ use arrayvec::ArrayString;
 use std::mem;
 use arrayvec::CapacityError;
 
-use std::collections::HashMap;
-
-
 #[test]
 fn test_simple() {
     use std::ops::Add;
@@ -523,6 +520,7 @@ fn array_clone_from() {
 #[cfg(feature="std")]
 #[test]
 fn test_string() {
+    use std::collections::HashMap;
     use std::error::Error;
 
     let text = "hello world";
@@ -790,4 +788,11 @@ fn test_arraystring_zero_filled_has_some_sanity_checks() {
     let string = ArrayString::<4>::zero_filled();
     assert_eq!(string.as_str(), "\0\0\0\0");
     assert_eq!(string.len(), 4);
+}
+
+#[test]
+fn try_from_vec_returns_correct_values() {
+    use core::convert::TryFrom;
+    assert!(ArrayVec::<_, 1>::try_from(vec![1]).is_ok());
+    assert!(ArrayVec::<_, 1>::try_from(vec![1, 2]).is_err());
 }