Taking view from Fixedarray

[Yu-zh]

This PR implements taking view from FixedArray.

Solves #1626

[peter-jerry-ye-code-review]

Unsafe cast function lacks proper type safety documentation

Category
Correctness
Code Snippet
fn[T] unsafe_cast_fixedarray_to_uninitializedarray(
arr : FixedArray[T],
) -> UninitializedArray[T] = "%identity"
Recommendation
Add comprehensive documentation explaining the safety contract and invariants that must be maintained when using this function. Consider adding a comment about why this cast is safe in this specific context.
Reasoning
Unsafe operations should be thoroughly documented to prevent misuse. The function name has a typo ('Unitialized' should be 'Uninitialized') and lacks documentation about when it's safe to use.

Duplicated bounds checking logic between ArrayView::sub and FixedArray::sub

Category
Maintainability
Code Snippet
let end = match end {
None => len
Some(end) => if end < 0 { len + end } else { end }
}
let start = if start < 0 { len + start } else { start }
guard start >= 0 && start <= end && end <= len else {
abort("View index out of bounds")
}
Recommendation
Extract the bounds checking and negative index handling logic into a shared helper function that both ArrayView::sub and FixedArray::sub can use to reduce code duplication.
Reasoning
The exact same bounds checking logic appears in both functions, violating the DRY principle and making maintenance harder. A shared helper would ensure consistent behavior and reduce the chance of bugs.

Inconsistent error messages between similar functions

Category
Correctness
Code Snippet
guard start >= 0 && start <= end && end <= len else {
abort("View index out of bounds")
}
Recommendation
Use the same error message format as ArrayView::sub or create a standardized error message function to ensure consistency across the codebase.
Reasoning
Different error messages for the same type of error can confuse users and make debugging harder. Consistent error messaging improves user experience and maintainability.

[coveralls]

Pull Request Test Coverage Report for Build 1229

Details

• 7 of 8 (87.5%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.002%) to 89.646%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
builtin/arrayview.mbt	7	8	87.5%

Totals
Change from base Build 1228:	-0.002%
Covered Lines:	9299
Relevant Lines:	10373

---

💛 - Coveralls

[peter-jerry-ye]

When will ArrayView become immutable?

[Yu-zh]

When will ArrayView become immutable?

The op_set method is already deprecated