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

Daryle Walker darylew at mac.com
Mon Aug 7 23:12:05 CDT 2017

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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