[Pitch #2] Add `isIdentical` Methods for Quick Comparisons to Concrete Types

[vanvoorden (Rick van Voorden)]

@xwu

@vanvoorden

We need a new API in standard library because there is no public API available today for product engineers to do this.

Is not x.span.isIdentical(to: y.span) a valid implementation of the proposed function for two arrays x and y?

Correct. This is a legit workaround for a missing isIdentical on Array. The bummer is that we are blocked on backdeploying the Array.span property:

Using `Span` on pre-26 Apple OS versions

Array.span, String.utf8.span and Substring.utf8.span aren't back-deployable due to the bridging changes they depend on.

The RFC implementation diff implementing isIdentical on Array is using _alwaysEmitIntoClient:

[StdLib][RFC][DNM] Add `isIdentical` Methods for Quick Comparisons to Array, ArraySlice, and ContiguousArray

So AFAIK we will have no runtime OS requirements on Array.isIdentical.