inout says it will copy into the function and copy back after the function is finished. But the order is unknown. So I think the example,
print(acopy) // prints "[1, 2, 99]" (e.g. a let variable changed!) i s a bug as the value changed inside of the function, before the function returns. Swift doc: “In-out parameters are passed as follows: 1 . When the function is called, the value of the argument is copied. 2 . In the body of the function, the copy is modified. 3 . When the function returns, the copy’s value is assigned to the original argument.” 摘录来自: Apple Inc. “The Swift Programming Language (Swift 2.2)”。 iBooks. Zhaoxin On Sun, Jun 12, 2016 at 9:27 AM, Karl Pickett via swift-users < swift-users@swift.org> wrote: > Wow there are some real doozy inout code examples in there, showing > aliasing much more fun than my snippet. Unfortunately I can't > understand anything else the doc is talking about. I guess I'll just > say a prayer and throw salt over my shoulder if using inout. > > On Sat, Jun 11, 2016 at 6:05 PM, Brent Royal-Gordon > <br...@architechies.com> wrote: > >> My recollection is that in Swift the subscript operator (`arr[2]` in > this case) can refer to the setter xor the getter, but not both within the > same statement. > > > > Quite to the contrary. Rather than using the setter directly, Swift > often uses `materializeForSet`, a combined get-and-set operation which is > much more efficient, particularly when assigning directly into arrays. To > keep from having to use very slow access all the time, it imposes a rule > (which is not and cannot be enforced by the compiler) that you can't hold > two mutable references to overlapping storage simultaneously, or they may > do strange things like lose some of the writes you make. > > > > Here's an old design document discussing some things in this area: < > https://github.com/apple/swift/blob/73841a643c087e854a2f62c7e073317bd43af310/docs/proposals/Accessors.rst> > I'm not sure how authoritative it is, but it might give you an idea of > what's going on. > > > > -- > > Brent Royal-Gordon > > Architechies > > > _______________________________________________ > swift-users mailing list > swift-users@swift.org > https://lists.swift.org/mailman/listinfo/swift-users >
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