Store original ArrayVec inside UnderfilledError

src/arrayvec.rs

@@ -693,9 +693,9 @@ impl<T, const CAP: usize> ArrayVec<T, CAP> {
     /// capacity (see [`capacity`]).
     /// 
     /// [`capacity`]: #method.capacity
-    pub fn into_inner(self) -> Result<[T; CAP], UnderfilledError> {
+    pub fn into_inner(self) -> Result<[T; CAP], UnderfilledError<T, CAP>> {
         if self.len() < self.capacity() {
-            Err(UnderfilledError::new(self.capacity(), self.len()))
+            Err(UnderfilledError::new(self))
         } else {
             unsafe { Ok(self.into_inner_unchecked()) }
         }

src/errors.rs

@@ -4,6 +4,8 @@ use std::any::Any;
 #[cfg(feature="std")]
 use std::error::Error;
 
+use crate::ArrayVec;
+
 /// Error value indicating insufficient capacity
 #[derive(Clone, Copy, Eq, Ord, PartialEq, PartialOrd)]
 pub struct CapacityError<T = ()> {
@@ -48,23 +50,24 @@ impl<T> fmt::Debug for CapacityError<T> {
 }
 
 /// Error value indicating that capacity is not completely filled
-#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
-pub struct UnderfilledError {
-    capacity: usize,
-    len: usize,
-}
+#[derive(Clone, Debug, Eq, Ord, PartialEq, PartialOrd)]
+pub struct UnderfilledError<T, const CAP: usize>(ArrayVec<T, CAP>);
+
+impl<T, const CAP: usize> UnderfilledError<T, CAP> {
+    pub const fn new(inner: ArrayVec<T, CAP>) -> Self {
+        Self(inner)
+    }
 
-impl UnderfilledError {
-    pub const fn new(capacity: usize, len: usize) -> Self {
-        Self { capacity, len }
+    pub fn take_vec(self) -> ArrayVec<T, CAP> {
+        self.0
     }
 }
 
 #[cfg(feature="std")]
-impl Error for UnderfilledError {}
+impl<T: fmt::Debug, const CAP: usize> Error for UnderfilledError<T, CAP> {}
 
-impl fmt::Display for UnderfilledError {
+impl<T, const CAP: usize> fmt::Display for UnderfilledError<T, CAP> { 
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "capacity is not filled: expected {}, got {}", self.capacity, self.len)
+        write!(f, "capacity is not filled: expected {}, got {}", CAP, self.0.len())
     }
 }

tests/tests.rs

@@ -456,7 +456,8 @@ fn test_insert() {
 fn test_into_inner_1() {
     let mut v = ArrayVec::from([1, 2]);
     v.pop();
-    assert_eq!(v.into_inner(), Err(UnderfilledError::new(2, 1)));
+    let u = v.clone();
+    assert_eq!(v.into_inner(), Err(UnderfilledError::new(u)));
 }
 
 #[test]