> On 06 Dec 2017, at 20:54, Joe DeCapo via swift-evolution > <email@example.com> wrote: > > >> On Dec 6, 2017, at 12:39 PM, Thorsten Seitz via swift-evolution >> <firstname.lastname@example.org <mailto:email@example.com>> wrote: >> >> IUO is Swift’s equivalent to a null pointer and those are a _hole_ in the >> type system (this applies to all type systems having an equivalent to the >> null pointer). That is why such types are marked with "!“ in Swift. >> This does not mean that Swift has no type system but that it’s type system >> has carefully marked holes. > > But the types are only marked with "!" at the declaration site, just as types > conforming to DynamicMemberLookup and DynamicCallable would be marked at the > declaration site. There's no more indication at the call site that something > is an IUO than there would be for something conforming to these protocols. > They both require inspecting the type itself.
But IUO’s are marked with an “!” to differentiate it from a normal type, where as DynamicMemberLookup is just a normal protocol conformance. I would be curious as to what you think of this idea ? Would this still be too much of a constraint just to make sure that when people use this they’re explicitly aware of what they’re doing? : https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20171204/042015.html
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