ArrayView::join and FixedArray::join

[ethereal-dream]

Adding ArrayView::join and FixedArray::join functions makes it convenient to concatenate strings within an array into a single complete string.

[peter-jerry-ye-code-review]

ArrayView::join creates unnecessary intermediate array

Category
Performance
Code Snippet
pub fn View::join(self : ArrayView[String], separator : String) -> String {
let array = self.to_array()
@string.concat(array, separator~)
}
Recommendation
Implement direct string concatenation similar to FixedArray::join to avoid intermediate array allocation
Reasoning
Creating a new array just to join strings is inefficient as it requires additional memory allocation and copying. The implementation could directly iterate over the view and build the result string, similar to how FixedArray::join does it.

Inconsistent parameter types between FixedArray::join and ArrayView::join

Category
Maintainability
Code Snippet
fn FixedArray::join(self : FixedArray[String], separator : @string.View)
fn View::join(self : ArrayView[String], separator : String)
Recommendation
Use consistent parameter types for separator across both implementations, preferably @string.View for better performance
Reasoning
Using different types for the same parameter in similar functions makes the API less predictable and harder to use. @string.View is likely more efficient as it avoids copying strings.

FixedArray::join could be simplified by extracting the string building logic

Category
Maintainability
Code Snippet
pub fn FixedArray::join(...) {
// ... complex string building logic ...
}
Recommendation
Extract the string building logic into a separate private function that can be shared between different join implementations
Reasoning
The string building logic is relatively complex and could be reused. Extracting it would make the code more maintainable and could enable sharing the implementation with ArrayView::join.

[coveralls]

Pull Request Test Coverage Report for Build 6808

Details

• 0 of 10 (0.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.1%) to 92.865%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
array/view.mbt	0	1	0.0%
array/fixedarray.mbt	0	9	0.0%

Totals
Change from base Build 6807:	-0.1%
Covered Lines:	6221
Relevant Lines:	6699

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💛 - Coveralls

[peter-jerry-ye]

@Yu-zh asked whether we should be using View instead of String.

I think maybe we can use @string.View for separator, but keep T[String] for this signature.

[ethereal-dream]

When using @string.View for separator, what should I do with string.write_string(separator) since there doesn't seem to be a write_view function?

[peter-jerry-ye]

I think you can simply call to_string on the view. The support for view on the string builder would come later as its currently blocked by how the core package is organize, which I assume would still need a few weeks.