[swift-evolution] Proposal: Introduce User-defined "Dynamic Member Lookup" Types

[Magnus Ahltorp]

> 4 Dec. 2017 03:54 Thorsten Seitz via swift-evolution <swift-evolution at swift.org> wrote:
> 
> The difference is that IUOs are marked by a "!“ whereas dynamic member lookups look just like normal member lookups but unlike them can fail.

IUOs are not marked with an "!" by the caller, that's what makes them implicit. They *are* marked at the declaration, but so would dynamic member lookups be.

/Magnus