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IBM Cloud Functions Adds Support for Swift 4.2

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What’s happening with IBM Cloud Functions and Swift?

I’m excited to announce that IBM Cloud Functions officially supports Swift 4.2, which has been optimized for latency and local caching.

The new Swift 4.2 runtime leverages a new web proxy built with Go that replaces the previous Python web proxy. The web proxy allows action invocations to respond faster by providing lower latency for blocking calls. In addition, the web proxy provides some local caching on container re-use when hitting a warm invocation. Since the Swift program doesn’t exit after the invocation returns the result, the next invocation can take advantage of local caching such as global instances in memory or connections pools.

Ready to try it out?

Swift 4 offers the ability to use Codable types for input and output. In this example, the function takes a Codable “Input” and responds with a Codable “Output.”

  1. Create the following Swift file.

    struct Input: Codable {
    let name: String?
    struct Output: Codable {
    let body: String
    func main(param: Input, completion: (Output?, Error?) -> Void) -> Void {
    let result = Output(body: "Hello \(param.name ?? "IBM Cloud")!")
    completion(result, nil)
  2. Create the helloSwift action.ibmcloud fn action update helloSwift main.swift --kind swift:4.2 --web true
  3. Invoke the action.

    ibmcloud fn action invoke helloSwift -r
    "body": "Hello IBM Cloud!"
  4. Get the URL for the web action.

    ibmcloud fn action get helloSwift --url


Using a single file is recommended only for the development of quick demos. For production, it is better to pre-compile your Swift action as this avoids large latency on cold starts. It also allows you to compile your code and leverage any third-party libraries and dependencies.

How much faster is Swift 4.2?

Swift 4.2 is much faster than Swift 3.1.1 or Swift 4.1 as you can see in the graph below comparing warm invocation performance. Start new projects using Swift 4.2 or migrate any existing actions.

How do I learn more?

To set up a project and compile your Swift 4.2 Actions, check out the IBM Cloud Functions documentation.

Senior Technical Staff Member (STSM) - IBM Cloud Functions

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