Unclear results of trimming function

Simulor · January 18, 2022, 12:25pm

Hello!
The question is about this function and it's results:

apple/swift-algorithms/blob/main/Guides/Trim.md

# Trim

[[Source](https://github.com/apple/swift-algorithms/blob/main/Sources/Algorithms/Trim.swift) |
 [Tests](https://github.com/apple/swift-algorithms/blob/main/Tests/SwiftAlgorithmsTests/TrimTests.swift)]

Returns a `SubSequence` formed by discarding all elements at the start and end 
of the collection which satisfy the given predicate.

This example uses `trimming(while:)` to get a substring without the white space 
at the beginning and end of the string.

```swift
let myString = "   hello, world  "
print(myString.trimming(while: \.isWhitespace)) // "hello, world"

let results = [2, 10, 11, 15, 20, 21, 100].trimming(while: { $0.isMultiple(of: 2) })
print(results) // [11, 15, 20, 21]
```

## Detailed Design

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Could someone explain me please, why in results do we have "20"?
I thought it's just comment issue, but when I've checked it, it returns [11, 15, 20, 21]
100.isMultiple(of: 2) //true
20.isMultiple(of: 2) //true

I've expected results: [11, 15, 21]

Is this an issue or I didn't understand correctly how should it work?

Avi · January 18, 2022, 12:26pm

The sample code trims until reaches a number that isn't a multiple of two. As 20 is bracketed by odd numbers, it remains in the result.

Simulor · January 18, 2022, 1:47pm

Thanks for the explanation!
I've forgot the most important think... This is not a filter, it's trimming :)