feat(corelib): snapshot fixed-size array iterator

[cairolover]

Adds IntoIter and Iterator implementations for the fixed-size array [T; SIZE] type.

I am encountering issues where the trait implementation cannot be found unless

1. explicitly imported
2. if I define the implementation next to the definition of the Iterator trait.

tracking bug in #6943

[reviewable-StarkWare]

This change is 

[cairolover]

demonstrates the requirement for an explicit import

[orizi]

it isn't required - or at least it really shouldn't.

[orizi]

Reviewed all commit messages.
Reviewable status: 0 of 3 files reviewed, 3 unresolved discussions (waiting on @cairolover)

---

a discussion (no related file):
the return value for fixed sized span should probably not be a snapshot - probably means we need a more explicit definition for this.

---

corelib/src/array.cairo line 725 at r1 (raw file):

        crate::array::EmptyFixedSizeArrayImpl::<T>::span(@self).into_iter()
    }
}

and move to near Iterator trait defintion (as it is for a language construct defintion), so it won't require an explicit import.

Suggestion:

impl FixedSizeArrayIntoIterator<
    T, const SIZE: usize, +Drop<T>,
> of crate::iter::IntoIterator<[T; SIZE]> {
    type IntoIter = crate::array::SpanIter<T>;
    fn into_iter(self: [T; SIZE]) -> Self::IntoIter {
        self.span().into_iter()
    }
}

[orizi]

it isn't required - or at least it really shouldn't.

[cairolover]

Reviewable status: 0 of 4 files reviewed, 2 unresolved discussions (waiting on @orizi)

---

corelib/src/array.cairo line 725 at r1 (raw file):

Previously, orizi wrote…

and move to near Iterator trait defintion (as it is for a language construct defintion), so it won't require an explicit import.

This unfortunately does not work as I'm getting:

Cannot infer negative impl in \`core::array::FixedSizeArrayToSpan::<T, SIZE, \_>\` as it contains the unresolved type \`\[T; SIZE\]\`

hence why I was using two impls, for the empty-sized and non-empty FixedSizeArray

[cairolover]

Reviewable status: 0 of 4 files reviewed, 2 unresolved discussions (waiting on @orizi)

---

a discussion (no related file):

Previously, orizi wrote…

the return value for fixed sized span should probably not be a snapshot - probably means we need a more explicit definition for this.

can you expand on this? I'm not sure to understand

[orizi]

Reviewed all commit messages.
Reviewable status: 0 of 4 files reviewed, 3 unresolved discussions (waiting on @cairolover)

---

corelib/src/iter/traits/iterator.cairo line 33 at r2 (raw file):

        self.span().into_iter()
    }
}

This probably additionally requires a Desnap iterator of iterator - since iteration on flat-size-array should be denapped.

with the additional @ the type is now more correct.

Suggestion:

impl FixedSizeArrayIntoIterator<
    T, const SIZE: usize, +Drop<T>,
> of crate::iter::IntoIterator<@[T; SIZE]> {
    type IntoIter = crate::array::SpanIter<T>;
    fn into_iter(self: [T; SIZE]) -> Self::IntoIter {
        self.span().into_iter()
    }
}

[cairolover]

Reviewable status: 0 of 4 files reviewed, 3 unresolved discussions (waiting on @orizi)

---

corelib/src/iter/traits/iterator.cairo line 33 at r2 (raw file):

Previously, orizi wrote…

This probably additionally requires a Desnap iterator of iterator - since iteration on flat-size-array should be denapped.

with the additional @ the type is now more correct.

Still getting the issue about:

Cannot infer negative impl in `core::array::FixedSizeArrayToSpan::<T, SIZE, _>` as it contains the unresolved type `[T; SIZE]`

[orizi]

Reviewed all commit messages.
Reviewable status: 0 of 4 files reviewed, 3 unresolved discussions (waiting on @cairolover)

---

corelib/src/iter/traits/iterator.cairo line 33 at r2 (raw file):

Previously, cairolover (cairolover) wrote…

Still getting the issue about:

Cannot infer negative impl in `core::array::FixedSizeArrayToSpan::<T, SIZE, _>` as it contains the unresolved type `[T; SIZE]`

request the impl for ToSpan by adding:
+core::array::ToSpanTrait<[T; SIZE>`

[cairolover]

Reviewable status: 0 of 4 files reviewed, 3 unresolved discussions (waiting on @orizi)

---

corelib/src/iter/traits/iterator.cairo line 33 at r2 (raw file):

Previously, orizi wrote…

request the impl for ToSpan by adding:
+core::array::ToSpanTrait<[T; SIZE>`

Done.

Works fine now. Although, it requires explicit cast of a [T; usize] into a @[T; usize] when using iter methods

[orizi]

Reviewed 1 of 3 files at r4, all commit messages.
Reviewable status: 1 of 4 files reviewed, 3 unresolved discussions (waiting on @cairolover)

---

corelib/src/iter/traits/iterator.cairo line 33 at r2 (raw file):

Previously, cairolover (cairolover) wrote…

Done.

Works fine now. Although, it requires explicit cast of a [T; usize] into a @[T; usize] when using iter methods

to be expected - as i said earlier - this would probably require us having a desnap of an iterator - so that we'd be able to have the value of the iterator properly work.

---

corelib/src/test/language_features/for_test.cairo line 68 at r4 (raw file):

    assert_eq!(sum, 46);
}

no need here - this is a test for the for concept - this adds nothing specific for the test.

---

corelib/src/test/array_test.cairo line 221 at r4 (raw file):

        i += 1;
    }
}

Suggestion:

#[test]
fn test_empty_fixed_size_array_iterator() {
    let mut input: [usize; 0] = [];
    assert_eq!((@input).into_iter().next(), Option::None);
}

[cairolover]

Reviewable status: 1 of 4 files reviewed, 3 unresolved discussions (waiting on @orizi)

---

corelib/src/test/language_features/for_test.cairo line 68 at r4 (raw file):

Previously, orizi wrote…

no need here - this is a test for the for concept - this adds nothing specific for the test.

Done.

---

corelib/src/test/array_test.cairo line 221 at r4 (raw file):

        i += 1;
    }
}

Done.
I can't inline this in a single line as the value passed to next() must be an explicitly defined mutable variable. It would be nice to make this possible at the compiler level

[orizi]

Reviewed 1 of 4 files at r2, 2 of 2 files at r5, all commit messages.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @cairolover)

---

a discussion (no related file):

Previously, cairolover (cairolover) wrote…

can you expand on this? I'm not sure to understand

if i'm iterating over [1, 4 , 7] i should get 1 4 and 7 - not @1 @4 and @7

---

corelib/src/test/array_test.cairo line 210 at r5 (raw file):

        i += 1;
    }
}

Suggestion:

    let mut iter = (@[10_usize, 11, 12, 13]).into_iter();
    assert_eq!(iter.next(), Option::Some(@10));
    assert_eq!(iter.next(), Option::Some(@11));
    assert_eq!(iter.next(), Option::Some(@12));
    assert_eq!(iter.next(), Option::Some(@13));
    assert!(iter.next().is_none());
}

[cairolover]

Reviewable status: 3 of 4 files reviewed, 2 unresolved discussions (waiting on @orizi)

---

corelib/src/test/array_test.cairo line 210 at r5 (raw file):

        i += 1;
    }
}

Done.

[orizi]

Reviewed 1 of 1 files at r6, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @cairolover)

---

a discussion (no related file):
@gilbens-starkware for 2nd eye.

[orizi]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @cairolover)

---

a discussion (no related file):

Previously, orizi wrote…

@gilbens-starkware for 2nd eye.

.

[gilbens-starkware]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @cairolover)