Brent Simmons
Filed as rdar://22109003
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@eridius It just has to check once that EmailMessage is a NodeRepresentedObject. It shouldn't have to check for each item.
Kevin Ballard
@brentsimmons It’s not a type-check. The in-memory representation is different. It has to allocate a new array with the new values.
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@eridius There may be plenty of benefits to that — but it makes app-writing a little more difficult. - View other replies
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@brentsimmons It seems to me the occasional `foo.map({$0})` is a small price to pay for avoiding hidden performance gotchas. -
@eridius I’d argue that, instead, there shouldn’t be a hidden performance gotcha. - View other replies
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@brentsimmons That would be nice, but the only way to solve this without a new array basically requires all protocols to use message-passing -
@eridius Works for me! - View other replies
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@brentsimmons Message passing is a performance gotcha :P - View other replies
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@eridius But barely. We can write fast apps in Objective-C. - View other replies
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@brentsimmons Yeah, but you should be able to write faster ones in Swift. - View other replies
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@brentsimmons Non-@objc protocols use a virtual function table (called a protocol witness table) rather than message-passing. -
@brentsimmons This means that objects typed as EmailMessage have a different table pointer than those typed as NodeRepresentedObject.
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