[swift-evolution] Add ability to validate collection indices

[Daniel Vollmer]

Hi,

> On 16 Dec 2016, at 14:56, Alexey Komnin via swift-evolution <swift-evolution at swift.org> wrote:

[snip]

> What do you think? I feel, like we should discuss it before I
> formalize it as a proposal.

I think this is a fruitless attempt, as even if the indices are still valid,
they may not refer to the same elements they referenced before the mutation.

Of course, mutating methods should state whether the invalidate existing
indices, but I think that’s about the best that can be reasonably done.

	Daniel.