[swift-evolution] How does "Sequence.joined" work?

[Félix Cloutier]

All this means is that `joined()` does not create an array that contains the new result. It's only as magic as the COW semantics on arrays.

> Le 7 août 2017 à 21:12, Daryle Walker via swift-evolution <swift-evolution at swift.org> a écrit :
> 
> I was looking at random items at SwiftDoc.org <http://swiftdoc.org/>, and noticed the “FlattenBidirectionalCollection” structure. It helps implement some versions of “joined” from Sequence (probably when the Sequence is also a BidirectionalCollection). The directions for the type state that “joined” does not create new storage. Then wouldn’t it have to refer to the source objects by reference? How; especially how does it work without requiring a “&” with “inout” or how it works with “let”-mode objects? Or am I misunderstanding how it works behind the covers?
> 
> (If there is a secret sauce to have one object refer to another without “&”/“inout”/“UnsafeWhateverPointer”, I like to know. It may help with implementing an idea. The idea involves extending the language, so “compiler magic” that the user can’t access is OK; I’d just claim to use the same sauce in my proposal.)
> 
> — 
> Daryle Walker
> Mac, Internet, and Video Game Junkie
> darylew AT mac DOT com 
> 
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