extension NonEmpty where C: MutableCollection, C.Index == Int isn't safe

[Ole Begemann]

Your extension NonEmpty where C: MutableCollection, C.Index == Int breaks for base collections that have integer indices that don't necessarily start at zero, such as ArraySlice or Data.

Example: this test crashes with "Fatal error: Index out of bounds".

  func testMutableCollectionWithArraySlice() {
    let numbers = Array(1...10)
    var xs = NonEmpty(0, numbers[5...])
    xs[1] = 43
    XCTAssertEqual(43, xs[1])
  }

[Brandon Williams]

lol you're fast, we haven't even announced this yet! 🤫

[Ole Begemann]

Lol, sorry. 😜 I didn't even notice this was brand new. I watched your last episode yesterday and heard you talk about non-empty collections and that inspired me to start writing this myself. When I got stuck it occurred to me I should look whether you guys had written a similar type and that's when I found this.