Re: memmove in Swift
Re: memmove in Swift
- Subject: Re: memmove in Swift
- From: Quincey Morris <email@hidden>
- Date: Wed, 20 Aug 2014 21:25:44 -0700
On Aug 20, 2014, at 20:32 , Gerriet M. Denkmann <email@hidden> wrote:
> But I thought that maybe memmove might be more efficient:
>
> let dest : UnsafeMutablePointer<Void> = arr + lowerIndex + 1
Er, no. There are multiple things wrong with this:
— There’s nothing in the Swift array API contract that says that elements are stored in a contiguous block of memory, or even in several blocks of memory
— Even if they were, there’s nothing that says how they’re laid out in that memory
— Even if there was, there’s nothing that gives you access to that memory (well, AFAIK)
— Even if there was, the use of ‘arr’ as a pointer to the start of the memory is a C-ism, and doesn’t apply to an array variable in Swift.
If you want to do this sort of thing, you’re going to have to cause your own block of memory to be allocated (e.g. in a NSData object). Alternatively, you could code the move as you originally did, and trust that at some point the Swift compiler will understand what you’re doing and optimize it for you.
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