> On 04 Nov 2016, at 13:59, Ryan Lovelett via swift-users
> <swift-users@swift.org> wrote:
>
> struct Foo {
> init(from buffer: Data) {
> bar = integer(withBytes: Array(buffer[4..<6]))
> baz = integer(withBytes: Array(buffer[6..<8]))
> ...
> }
>
> let d = Data(count: Int(3e+8))
> let f = Foo(from: d)
>
> Did I just make two copies of the `Data`? How would I investigate this
> to understand it?
I often end up “printing” the addresses or using GDB to take an inside look.
However those snippets of inside information obtained that way are not
necessary useful outside the specific problem that was studied.
As Brent already hinted: the compiler will generate different code in different
situations. And for an outsider it is not always easy to understand why which
code was generated.
The best approach imo is to “trust” the compiler and only start such
investigations if you experience performance problems.
One thing that tripped me up: if you use inout variables, the observers will be
triggered once the function completes. Even if the function never changed the
data referred to. (This is now documented behaviour)
>
> I _think_ that if I made it `inout` then it would not make a copy but
> now the data buffer is mutable. I want it to be clear I'm not mutating
> the buffer inside the initializer but I also want to be sure I'm not
> making a copy of the buffer either.
>
> Help?
>
> --
> Ryan Lovelett
> r...@lovelett.me
> _______________________________________________
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> swift-users@swift.org
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Regards,
Rien
Site: http://balancingrock.nl
Blog: http://swiftrien.blogspot.com
Github: http://github.com/Swiftrien
Project: http://swiftfire.nl
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