Add accessor with bounds check to Array

[Chris_Lattner3 (Chris Lattner)]

@jawbroken

It's also in the commonly rejected list together with the rationale.

To be precise, the idea of changing the type of the unlabelled subscript on Array to an optional is on the commonly rejected list, whereas this thread is about adding a new accessor with bounds checking. There has been a lot of past discussion about this though.

Agreed. It would be nice to clarify the wording on the commonly rejected list from "Make Array<T> subscript access return" to "Change Array<T> subscript access to return" to clarify this.

@jawbroken

I wouldn't necessarily be opposed to a separate labelled subscript that returns an optional. I sometimes define this subscript myself to clean up multi-dimensional array processing code where you need to look at neighbouring entries. Nil coalescing is a blessing for code clarity in this situation, because the alternative is a lot of specially casing or conditional testing for the edges.

Agreed, the most frequently suggested spelling for this is: yourArray[safe: idx], which seems great to me. I am very +1 for adding this.

-Chris