Re: [swift-users] Mapping C semantics to Swift

[Ken Burgett via swift-users]

On 2016-05-20 08:55, Jens Alfke wrote:

On May 20, 2016, at 7:33 AM, Ken Burgett via swift-users
 wrote:

the required C struct morphs into a Swift class, with a member
function 'as_C_byte_array' which answers an array of the required
form. Internally, this function will shift and mask class attributes
in order to build the necessary result.


It would be nice to see Swift acquire structured-data I/O APIs as
found in languages like Ruby and Python — these take a printf-like
format string and parameters, but read and write values in binary. The
format syntax offers modifiers to specify things like byte order,
string encoding, etc. This is so much more reliable and readable than
doing the encoding by hand.

—Jens

Hi Jens,

I understand the value of strong typing from a runtime point of view, 
but I really miss the quickness and simplicity of writing a class in 
Ruby, where duck-typing is king.

--
Ken Burgett
Principal Software Engineer
Email: k...@iotone.io
Office: 530.693.4449
Mobile: 831.332.6846
URL: www.iotone.co
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Re: [swift-users] Mapping C semantics to Swift

[Jens Alfke via swift-users]

> On May 20, 2016, at 7:33 AM, Ken Burgett via swift-users 
>  wrote:
> 
> the required C struct morphs into a Swift class, with a member function 
> 'as_C_byte_array' which answers an array of the required form.  Internally, 
> this function will shift and mask class attributes in order to build the 
> necessary result.

It would be nice to see Swift acquire structured-data I/O APIs as found in 
languages like Ruby and Python — these take a printf-like format string and 
parameters, but read and write values in binary. The format syntax offers 
modifiers to specify things like byte order, string encoding, etc. This is so 
much more reliable and readable than doing the encoding by hand.

—Jens___
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Re: [swift-users] Mapping C semantics to Swift

[Ramakrishna Mallireddy via swift-users]

An working example,

let fm = NSFileManager.defaultManager()

  var mh = mach_header()   // Defined as C struct, 

  var lc = load_command()  // Defined as C struct 

  var location = 0

  if let data = fm.contentsAtPath("home/user/projects/some.o") {

data.getBytes(, length: sizeof(mach_header))

location += sizeof(mach_header)

data.getBytes(, range: NSRange(location: location, length: sizeof(
load_command)) )

location += sizeof(load_command)

}

-Rk

On Thu, May 19, 2016 at 10:52 PM, Joe Groff via swift-users <
swift-users@swift.org> wrote:

>
> > On May 19, 2016, at 10:00 AM, Ken Burgett via swift-users <
> swift-users@swift.org> wrote:
> >
> > I would like to know if a struct in Swift has any guarantee of
> contiguity, like a struct in C.  I am attempting to port a C program that
> makes many assumptions about the underlying semantics of C structs, and
> does things like overlaying an array over the struct using a cast, and then
> performs and cryptographic hashing of the entire struct by treating it as
> an array.
> >
> > 1.  I a Swift struct contiguous?
> >
> > 2.  If 1 above is true, can I somehow cast an array over the struct?
>
> Swift structs have unspecified layout. If you depend on a specific layout,
> you should define the struct in C and import it into Swift for now.
>
> -Joe
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Re: [swift-users] Mapping C semantics to Swift

[Joe Groff via swift-users]

> On May 19, 2016, at 10:00 AM, Ken Burgett via swift-users 
>  wrote:
> 
> I would like to know if a struct in Swift has any guarantee of contiguity, 
> like a struct in C.  I am attempting to port a C program that makes many 
> assumptions about the underlying semantics of C structs, and does things like 
> overlaying an array over the struct using a cast, and then performs and 
> cryptographic hashing of the entire struct by treating it as an array.
> 
> 1.  I a Swift struct contiguous?
> 
> 2.  If 1 above is true, can I somehow cast an array over the struct?

Swift structs have unspecified layout. If you depend on a specific layout, you 
should define the struct in C and import it into Swift for now.

-Joe
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