olbrichj

Promise() { fulfill, reject in
    // code       
}

olbrichj

Promise() { fulfill, reject in
    return "Hello World" //or other async code           
}

olbrichj

fetchPromise().then { value in
  // do something
}.catch { error in {
  // in case of error  
}

olbrichj

fetchPromise().then { value in
    return fetchPromise2(value)
}.then { value in
    // do something
}.catch { error in 
    // error 
}

olbrichj

fetchPromise().then { value in
    return errorPromise(value) // this will throw an error
}.then { value in
    //this will not execute on error
}.catch { error in
    //we got an error 
}

olbrichj

use_frameworks!

target "target" do
  pod "PromiseKit", "~> 6.0"
end

olbrichj

github "mxcl/PromiseKit" ~> 6.0

olbrichj

package.dependencies.append(
    .Package(url: "https://github.com/mxcl/PromiseKit", majorVersion: 6)
)

olbrichj

func fetch(url: URL) -> Promise<Data> {
    return Promise { seal in
        URLSession.shared.dataTask(with: url!) { data, _, error in
            seal.resolve(data, error)
        }.resume()
    }
}

fetch(url: <backendURL>).then { data in
    return JSONParsePromise(data) // we skip the wrapping of JSONParsing

olbrichj

Guarantee { seal in
    seal("Hello World")
}