I have a transformation function that takes in data, executes some instructions, and returns an output. This function is dynamic and not shipped with the binary. Currently, I’m executing it using JavaScriptCore.JSContext, which works well, but the function itself is written in JavaScript.
Is there a way to achieve something similar using Swift – such as executing a dynamic Swift script, either directly or through other means? I know this is possible on macOS, but I’m not sure about iOS. I’ve also heard that extensions might open up some possibilities here. Any insights or alternative approaches would be appreciated.
It’s certainly possible, but probably more hassle than it’s worth.
Specifically, Swift supports compiling to WebAssembly (Wasm) [1] and you could then run the Wasm instructions yourself. However, this is much more difficult than the equivalent path with JavaScriptCore because:
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JavaScriptCore can interpret JavaScript directly. In Swift you’d have to include a copy of the Swift compiler within your app.
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Additionally, there’s no built-in Wasm runtime, so you’d have to write or acquire one of those.
Of these, the second point is less of an issue. Wasm runtimes are relatively small and easy to maintain. Indeed, there’s a default one featured on the Swift website [2].
The first point, however, is much more complex. The Swift compiler is big and complicated, and successfully embedding it in an iOS app would not be trivial.
Finally, there’s the App Review side of this. I don’t work for App Review, and thus can’t make definitive statements on their behalf. However, the App Review Guidelines do place restrictions on downloadable code, so I encourage you to read those.
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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
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[1] See Swift.org > Getting Started with Swift SDKs for WebAssembly.
[2] WasmKit