chore!: Remove empty value from bounded vec (#4431)

# Description

## Problem\*
## Summary\*

Removes the `empty_value` field from the bounded vec. This muddies the
API and shouldn't be needed since we have `crate::unsafe::zeroed()`
instead.

## Additional Context



## Documentation\*

Check one:
- [ ] No documentation needed.
- [ ] Documentation included in this PR.
- [x] **[Exceptional Case]** Documentation to be submitted in a separate
PR.
  - Included in #4430

# PR Checklist\*

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

---------

Co-authored-by: Tom French <15848336+TomAFrench@users.noreply.github.com>
Co-authored-by: Tom French <tom@tomfren.ch>

noir_stdlib/src/collections/bounded_vec.nr

@@ -1,12 +1,12 @@
 struct BoundedVec<T, MaxLen> {
     storage: [T; MaxLen],
     len: u64,
-    empty_value: T,
 }
 
 impl<T, MaxLen> BoundedVec<T, MaxLen> {
-    pub fn new(initial_value: T) -> Self {
-        BoundedVec { storage: [initial_value; MaxLen], len: 0, empty_value: initial_value }
+    pub fn new() -> Self {
+        let zeroed = crate::unsafe::zeroed();
+        BoundedVec { storage: [zeroed; MaxLen], len: 0 }
     }
 
     pub fn get(mut self: Self, index: u64) -> T {
@@ -68,7 +68,7 @@ impl<T, MaxLen> BoundedVec<T, MaxLen> {
         self.len -= 1;
 
         let elem = self.storage[self.len];
-        self.storage[self.len] = self.empty_value;
+        self.storage[self.len] = crate::unsafe::zeroed();
         elem
     }
 

test_programs/noir_test_success/bounded_vec/src/main.nr

@@ -1,6 +1,6 @@
 #[test]
 fn test_vec_push_pop() {
-    let mut vec: BoundedVec<Field, 3> = BoundedVec::new(0);
+    let mut vec: BoundedVec<Field, 3> = BoundedVec::new();
     assert(vec.len == 0);
     vec.push(2);
     assert(vec.len == 1);
@@ -17,7 +17,7 @@ fn test_vec_push_pop() {
 
 #[test]
 fn test_vec_extend_from_array() {
-    let mut vec: BoundedVec<Field, 3> = BoundedVec::new(0);
+    let mut vec: BoundedVec<Field, 3> = BoundedVec::new();
     vec.extend_from_array([2, 4]);
     assert(vec.len == 2);
     assert(vec.get(0) == 2);
@@ -26,69 +26,69 @@ fn test_vec_extend_from_array() {
 
 #[test(should_fail_with="extend_from_array out of bounds")]
 fn test_vec_extend_from_array_out_of_bound() {
-    let mut vec: BoundedVec<Field, 2> = BoundedVec::new(0);
+    let mut vec: BoundedVec<Field, 2> = BoundedVec::new();
     vec.extend_from_array([2, 4, 6]);
 }
 
 #[test(should_fail_with="extend_from_array out of bounds")]
 fn test_vec_extend_from_array_twice_out_of_bound() {
-    let mut vec: BoundedVec<Field, 2> = BoundedVec::new(0);
+    let mut vec: BoundedVec<Field, 2> = BoundedVec::new();
     vec.extend_from_array([2]);
     assert(vec.len == 1);
     vec.extend_from_array([4, 6]);
 }
 
 #[test(should_fail)]
 fn test_vec_get_out_of_bound() {
-    let mut vec: BoundedVec<Field, 2> = BoundedVec::new(0);
+    let mut vec: BoundedVec<Field, 2> = BoundedVec::new();
     vec.extend_from_array([2, 4]);
     let _x = vec.get(2);
 }
 
 #[test(should_fail)]
 fn test_vec_get_not_declared() {
-    let mut vec: BoundedVec<Field, 2> = BoundedVec::new(0);
+    let mut vec: BoundedVec<Field, 2> = BoundedVec::new();
     vec.extend_from_array([2]);
     let _x = vec.get(1);
 }
 
 #[test(should_fail)]
 fn test_vec_get_uninitialized() {
-    let mut vec: BoundedVec<Field, 2> = BoundedVec::new(0);
+    let mut vec: BoundedVec<Field, 2> = BoundedVec::new();
     let _x = vec.get(0);
 }
 
 #[test(should_fail_with="push out of bounds")]
 fn test_vec_push_out_of_bound() {
-    let mut vec: BoundedVec<Field, 1> = BoundedVec::new(0);
+    let mut vec: BoundedVec<Field, 1> = BoundedVec::new();
     vec.push(1);
     vec.push(2);
 }
 
 #[test(should_fail_with="extend_from_bounded_vec out of bounds")]
 fn test_vec_extend_from_bounded_vec_out_of_bound() {
-    let mut vec: BoundedVec<Field, 2> = BoundedVec::new(0);
+    let mut vec: BoundedVec<Field, 2> = BoundedVec::new();
 
-    let mut another_vec: BoundedVec<Field, 3> = BoundedVec::new(0);
+    let mut another_vec: BoundedVec<Field, 3> = BoundedVec::new();
     another_vec.extend_from_array([1, 2, 3]);
 
     vec.extend_from_bounded_vec(another_vec);
 }
 
 #[test(should_fail_with="extend_from_bounded_vec out of bounds")]
 fn test_vec_extend_from_bounded_vec_twice_out_of_bound() {
-    let mut vec: BoundedVec<Field, 2> = BoundedVec::new(0);
+    let mut vec: BoundedVec<Field, 2> = BoundedVec::new();
     vec.extend_from_array([1, 2]);
 
-    let mut another_vec: BoundedVec<Field, 1> = BoundedVec::new(0);
+    let mut another_vec: BoundedVec<Field, 1> = BoundedVec::new();
     another_vec.push(3);
 
     vec.extend_from_bounded_vec(another_vec);
 }
 
 #[test]
 fn test_vec_any() {
-    let mut vec: BoundedVec<Field, 3> = BoundedVec::new(0);
+    let mut vec: BoundedVec<Field, 3> = BoundedVec::new();
     vec.extend_from_array([2, 4, 6]);
     assert(vec.any(|v| v == 2) == true);
     assert(vec.any(|v| v == 4) == true);
@@ -98,8 +98,8 @@ fn test_vec_any() {
 
 #[test]
 fn test_vec_any_not_default() {
-    let default_value = 1;
-    let mut vec: BoundedVec<Field, 3> = BoundedVec::new(default_value);
+    let default_value = 0;
+    let mut vec: BoundedVec<Field, 3> = BoundedVec::new();
     vec.extend_from_array([2, 4]);
     assert(vec.any(|v| v == default_value) == false);
-}
+}