Fix pre-checks in try_boxed_from_iter

Author: novacrazy

src/arr.rs

@@ -21,7 +21,6 @@
 /// * The `[T; N: ArrayLength]` and `[T; usize]` explicit forms are limited to `Copy` values. Use
 /// [`GenericArray::generate(|| value.clone())`](crate::GenericSequence::generate) for non-`Copy` items.
 /// * The `[T; usize]` explicit and `[0, 1, 2, 3]` implicit forms are limited to lengths supported by [`Const<U>`](typenum::Const)
-
 #[macro_export]
 macro_rules! arr {
     ($($x:expr),* $(,)*) => ( $crate::GenericArray::from_array([$($x),*]) );

src/impl_alloc.rs

@@ -91,8 +91,10 @@ impl<T, N: ArrayLength> GenericArray<T, N> {
 
         // pre-checks
         match iter.size_hint() {
-            (n, _) if n < N::USIZE => return Err(TryFromIterError::TooShort),
-            (_, Some(n)) if n > N::USIZE => return Err(TryFromIterError::TooLong),
+            // if the lower bound is greater than N, array will overflow
+            (n, _) if n > N::USIZE => return Err(TryFromIterError::TooLong),
+            // if the upper bound is smaller than N, array cannot be filled
+            (_, Some(n)) if n < N::USIZE => return Err(TryFromIterError::TooShort),
             _ => {}
         }