[swift-users] file io in Swift 2.2 for Linux (would like to be pointed in the right direction)

[Brent Royal-Gordon]

> Looks good, but you'll want some error handling. There's no clean way to integrate it with Generator because the protocol doesn't allow the implementation to throw, unfortunately. (I've run into the same problem building a Generator around a database query.) I think the best solution is to add a property that returns the NSStream.streamError, or a checkError() method that throws the current error if any, and have the caller use those at the end of the iteration.

You can do better.

	extension NSInputStream {
		// I will assume you already have a byteGenerator method (which you can use with a for loop)
		// with a checkError() method (which throws if the generation terminated due to an error). However, 
		// you've made these private, and will use them to implement this safe public API.
		public func withByteGenerator<R>(blockSize: Int = 1024, iterate: @noescape (NSInputStream.ByteGenerator) throws -> R) throws -> R {
			let generator = byteGenerator(blockSize: blockSize)
			let result = iterate(generator)
			try generator.checkError()
			return result
		}
	}

Now you write:

	guard let stream = NSInputStream(fileAtPath: path) else {
		…
	}
	try stream.withByteGenerator {
		// XXX This would all be more complicated if CharacterGenerator can throw, too.
		for (i, line) in LineGenerator(source: CharacterGenerator(source: $0, decoder: UTF8())).enumerate() {
			print("\(i+1): \(line)")
		}
	}

(I'm assuming that these generators take their almost-automatic Sequence conformance, of course.)

-- 
Brent Royal-Gordon
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