From bf491dce9595d0e37057ae6d6721eb7a83cec0e2 Mon Sep 17 00:00:00 2001
From: Leonid Logvinov <logvinov.leon@gmail.com>
Date: Mon, 6 May 2024 17:52:51 +0200
Subject: [PATCH] feat: implement `From` array trait for `BoundedVec` (#4927)

# Description

## Problem\*

Implementing a concise, single-line method for converting arrays to
BoundedVec would enhance usability.

## Summary\*

This pull request implements the `From` trait to enable
array-to-BoundedVec conversions, allowing for the following usage
```rust
let vec = BoundedVec::from([1, 2, 3]);
```

instead of:
```rust
let vec: BoundedVec<Field, 3> = BoundedVec::new();
vec.extend_from_array([1, 2, 3]);
```


## Additional Context



## Documentation\*

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# 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: Arkadiusz Konior <akonior@gmail.com>
---
 .../standard_library/containers/boundedvec.md | 14 ++++
 noir_stdlib/src/collections/bounded_vec.nr    | 71 ++++++++++++++++++-
 2 files changed, 84 insertions(+), 1 deletion(-)

diff --git a/docs/docs/noir/standard_library/containers/boundedvec.md b/docs/docs/noir/standard_library/containers/boundedvec.md
index cd0f725f870..ccce62562f8 100644
--- a/docs/docs/noir/standard_library/containers/boundedvec.md
+++ b/docs/docs/noir/standard_library/containers/boundedvec.md
@@ -196,6 +196,20 @@ Example:
 
 #include_code bounded-vec-extend-from-bounded-vec-example test_programs/noir_test_success/bounded_vec/src/main.nr rust
 
+### from_array
+
+```rust
+pub fn from_array<Len>(array: [T; Len]) -> Self
+```
+
+Creates a new vector, populating it with values derived from an array input. 
+The maximum length of the vector is determined based on the type signature.
+
+Example:
+```rust
+let bounded_vec: BoundedVec<Field, 10> = BoundedVec::from_array([1, 2, 3])
+```
+
 ### any
 
 ```rust
diff --git a/noir_stdlib/src/collections/bounded_vec.nr b/noir_stdlib/src/collections/bounded_vec.nr
index c6a3365a979..65f3716dd34 100644
--- a/noir_stdlib/src/collections/bounded_vec.nr
+++ b/noir_stdlib/src/collections/bounded_vec.nr
@@ -1,4 +1,4 @@
-use crate::cmp::Eq;
+use crate::{cmp::Eq, convert::From};
 
 struct BoundedVec<T, MaxLen> {
     storage: [T; MaxLen],
@@ -74,6 +74,13 @@ impl<T, MaxLen> BoundedVec<T, MaxLen> {
         self.len = new_len;
     }
 
+    pub fn from_array<Len>(array: [T; Len]) -> Self {
+        assert(Len <= MaxLen, "from array out of bounds");
+        let mut vec: BoundedVec<T, MaxLen> = BoundedVec::new();
+        vec.extend_from_array(array);
+        vec
+    }
+
     pub fn pop(&mut self) -> T {
         assert(self.len > 0);
         self.len -= 1;
@@ -107,6 +114,12 @@ impl<T, MaxLen> Eq for BoundedVec<T, MaxLen> where T: Eq {
     }
 }
 
+impl<T, MaxLen, Len> From<[T; Len]> for BoundedVec<T, MaxLen> {
+    fn from(array: [T; Len]) -> BoundedVec<T, MaxLen>  {
+        BoundedVec::from_array(array)
+    }
+}
+
 mod bounded_vec_tests {
     // TODO: Allow imports from "super"
     use crate::collections::bounded_vec::BoundedVec;
@@ -128,4 +141,60 @@ mod bounded_vec_tests {
 
         assert(bounded_vec1 != bounded_vec2);
     }
+
+    mod from_array {
+        use crate::collections::bounded_vec::BoundedVec;
+
+        #[test]
+        fn empty() {
+            let empty_array: [Field; 0] = [];
+            let bounded_vec = BoundedVec::from_array([]);
+
+            assert_eq(bounded_vec.max_len(), 0);
+            assert_eq(bounded_vec.len(), 0);
+            assert_eq(bounded_vec.storage(), empty_array);
+        }
+
+        #[test]
+        fn equal_len() {
+            let array = [1, 2, 3];
+            let bounded_vec = BoundedVec::from_array(array);
+
+            assert_eq(bounded_vec.max_len(), 3);
+            assert_eq(bounded_vec.len(), 3);
+            assert_eq(bounded_vec.storage(), array);
+        }
+
+        #[test]
+        fn max_len_greater_then_array_len() {
+            let array = [1, 2, 3];
+            let bounded_vec: BoundedVec<Field, 10> = BoundedVec::from_array(array);
+
+            assert_eq(bounded_vec.max_len(), 10);
+            assert_eq(bounded_vec.len(), 3);
+            assert_eq(bounded_vec.storage()[0], 1);
+            assert_eq(bounded_vec.storage()[1], 2);
+            assert_eq(bounded_vec.storage()[2], 3);
+        }
+
+        #[test(should_fail_with="from array out of bounds")]
+        fn max_len_lower_then_array_len() {
+            let _: BoundedVec<Field, 2> = BoundedVec::from_array([0; 3]);
+        }
+    }
+
+    mod trait_from {
+        use crate::collections::bounded_vec::BoundedVec;
+
+        #[test]
+        fn simple() {
+            let array = [1, 2];
+            let bounded_vec: BoundedVec<Field, 10> = BoundedVec::from(array);
+
+            assert_eq(bounded_vec.max_len(), 10);
+            assert_eq(bounded_vec.len(), 2);
+            assert_eq(bounded_vec.storage()[0], 1);
+            assert_eq(bounded_vec.storage()[1], 2);
+        }
+    }
 }