I can't find anything in the Swift book about io. Is there any generic protocol similar to Java's OutputStream or Go's Writer interface for writing a stream of bytes? If you are writing a class that returns a stream, do you need to write your own protocol or use an Objective C protocol?
To be clear am asking for a Swift native interface for this not because I avoiding using Objective C or Cocoa, but for a description of the expected behavior for Swift to Swift code going forward.
This is something the Swift docs are quiet about and I wanted to know more about so I looked into it.
There is a protocol, it's called Streamable
:
protocol Streamable {
func writeTo<Target : OutputStream>(inout target: Target)
}
OutputStream
:
protocol OutputStream {
func write(string: String)
}
write
allows an object to be written to.
String
conforms to both, making it easy to write to and from:
var target = String()
"this is a message".writeTo(&target)
println(target)
// this is a message
Writing to a file:
var msg = "this will be written to an output file"
msg.writeToFile("output.txt", atomically: false, encoding: NSUTF8StringEncoding, error: nil)
// creates 'output.txt' in the same folder as the executable
There is also writeToUrl
.
I assume those functions are all built on top of Cocoa streams, which have similar functionality:
var os = NSOutputStream(toFileAtPath: "output.txt", append: true)
os.scheduleInRunLoop(NSRunLoop.currentRunLoop(), forMode: NSDefaultRunLoopMode)
var msg = "a truly remarkable message"
var ptr:CConstPointer<UInt8> = msg.nulTerminatedUTF8
os.open()
os.write(ptr, maxLength: msg.lengthOfBytesUsingEncoding(NSUTF8StringEncoding))
os.close()
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