[swift-evolution] Low-level Swift

[Félix Cloutier]

It is. This:

> func foo(ptr: UnsafeMutablePointer<Int32>) {
> 	ptr.memory = 4
> 	ptr.memory = 5
> }

compiles to:

> define hidden void @_TF4test3fooFGVSs20UnsafeMutablePointerVSs5Int32_T_(i8* nocapture) #1 {
> entry:
>   %.value = bitcast i8* %0 to i32*
>   store i32 5, i32* %.value, align 4
>   ret void
> }

Notice how it's "missing" a store.

Félix

> Le 7 janv. 2016 à 15:54:36, Austin Zheng via swift-evolution <swift-evolution at swift.org> a écrit :
> 
> I'd think the hypothetical way in Swift to write to configuration registers would be to create an UnsafeMutablePointer<Int64> (or some other raw integer type) from a raw memory address, and then get/set the contents using the 'memory' property. Not sure if the compiler is "smart" enough to optimize out memory accesses made using that mechanism, although I would assume no.
> 
> Austin
> 
> On Thu, Jan 7, 2016 at 3:52 AM, Romain Goyet via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> Hi everyone,
> 
> In the introduction to Swift <https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/>, it is presented as an "industrial-quality systems programming language".
> According to Wikipedia <https://en.wikipedia.org/wiki/System_programming_language>, this means that I could expect to be able to write device drivers or operating systems in Swift.
> 
> However it seems like this claim is only partially true, since several important low-level features seem to be completely missing:
> 
> - Is it possible to generate volatile memory accesses <http://llvm.org/docs/LangRef.html#volatile-memory-accesses> in Swift? Writing device drivers is virtually impossible without a way to guarantee certain memory operations are actually made (and not optimized-out). 
> 
> - Is it possible to embed raw binary data in Swift? For example, an equivalent of the following C code "const int8_t foo[6] = {0x00,0x11,0x22,0x33,0x44,0x55};"? The simple Swift equivalent, "let foo: [Int8] = [0x0,0x1,0x2,0x3,0x4,0x6];" is obviously wildly different. Being able to embed raw binary data is very important in a low-level environment: for example, you may need to feed specific data to a device for an initialization sequence at a point where you don't have a filesystem available yet.
> 
> There might be other aspects that I'm overlooking right now, but I think that's enough to start a discussion: is Swift really meant to be a systems programming language?
> 
> Thanks,
> 
>  - Romain
> 
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