Swift: Convert structs and enums to NSData and vice-versa

func encode<T>(var value: T) -> NSData {
    return withUnsafePointer(&value) { p in
        NSData(bytes: p, length: sizeofValue(value))
    }
}

func decode<T>(data: NSData) -> T {
    let pointer = UnsafeMutablePointer<T>.alloc(sizeof(T.Type))
    data.getBytes(pointer)
    
    return pointer.move()
}

// Example:
enum Result<T> {
    case Success(T)
    case Failure
}

var res: Result<String> = .Success("yeah")

var data = encode(res)

var decoded: Result<String> = decode(data)

switch decoded {
case .Failure:
    "failure"
case .Success(let v):
    "success: \(v)" // => "success: yeah"
}

Great gist! With the deprecation of getBytes, should line 9 be...

data.getBytes(pointer, length: sizeof(T.Type))

Also, this seems to cause crashes if you have Strings in your struct.

@rob5408 works if you replace sizeof(T.Type) with just sizeof(T)

thank you
i also was trying to figure this out in the last days and now is working like a charm

@laszlokorte Thanks! As soon as I read your fix I realized how obvious it was. That said I would have NEVER figure that out. With Swift you get yourself thinking you don't have to worry about pointers then you let them in and immediately shoot your foot off.

I added a little error handling — see here.

I have an NSArray of Struct of which I writeToFile after encode each struct. If I read the saved plist in the same instance, I can read the data back perfectly but when I rerun and reload the data, it only partially decodes each struct. What gives?

Awesome; thank you!

It won't work, if you have an array in your struct.

Any reason why you would want to use this over Struct to NSData via NSJSONSerilization?

Yes, this use to work for me too. It works on simple structs but as it get more complex, nil is always returned. Anyone else experience this?

It seems to fail sometimes, returns nil once in a while even without changing anything on the struct

@RollingGoron speed