Rust-like error handling in Kotlin using `?`, is it possible?

Issue

The code below has several possible failures. For example, width could be null, or r could be false. In all cases, I should return a result.error() or something like that.

  override fun onMethodCall(@NonNull call: MethodCall, @NonNull result: Result) {
    if (call.method == "getPlatformVersion") {
      result.success("Android ${android.os.Build.VERSION.RELEASE}")
    } else if (call.method=="registerTexture") {
      val entry: TextureRegistry.SurfaceTextureEntry = texture_registry.createSurfaceTexture();
      val surfaceTexture = entry.surfaceTexture();
      //TODO: return non-sucess when no width and height passed
      val width: Int = call.argument("width")!!
      val height: Int = call.argument("height")!!
      surfaceTexture.setDefaultBufferSize(width, height)
      val response = HashMap<String, Long>()
      RendererPlugin.surfaceTextureMap.put(entry, surfaceTexture)
      val r = RendererPlugin.registerSurfaceTextureNativeHandler(entry.id(), surfaceTexture)
      if (!r) {
        Log.d(LOG_TAG, "attention: failed result from registerSurfaceTextureNativeHandler")
      }
      response.put("textureId", entry.id())
      result.success(response)
    }
  }

On Rust, I'd make all of this into a closure which results Result<(), Error> and then execute the closure inside onMethodCall and if I got an error, I'd return an error. Also, the closure would be full of calls ending with ? so it automatically returns the error that has a From<> implementation that converts to Error.

How can I do this efficiently in Kotlin? Is there a way to make a closure and also easily return success or error in this closure, and then based on this result I call result.sucess or result.error?

Solution

I hope this helps you.

Pay attention: I assume that result.success() accepts Any because you return String or HashMap as a parameter, but kotlin.Result doesn't have several generic success parameters. You can play with kotlin.Pair<A, B> as the success type of kotlin.Result :D

override fun onMethodCall(@NonNull call: MethodCall, @NonNull result: Result) {
    val finalResult: kotlin.Result<Any> = call.run {
        if (method == "getPlatformVersion") kotlin.Result.success("Android ${android.os.Build.VERSION.RELEASE}")
        else if (method == "registerTexture") {
            val entry: TextureRegistry.SurfaceTextureEntry = texture_registry.createSurfaceTexture();
            val surfaceTexture = entry.surfaceTexture();
            val width = argument("width") ?: return@run kotlin.Result.failure(IllegalArgumentException("width is null"))
            val height = argument("height") ?: return@run kotlin.Result.failure(IllegalArgumentException("height is null"))

            surfaceTexture.setDefaultBufferSize(width, height)
            val response = HashMap<String, Long>()
            RendererPlugin.surfaceTextureMap.put(entry, surfaceTexture)
            val r = RendererPlugin.registerSurfaceTextureNativeHandler(entry.id(), surfaceTexture)
            if (!r) return@run kotlin.Result.failure(IllegalArgumentException("r is false"))
            response.put("textureId", entry.id())
            kotlin.Result.success(response)
        }
        else kotlin.Result.failure(IllegalStateException("undefined call.method"))
    }

    with (finalResult) {
        onSuccess(result::success)
        onFailure(result::fail)
    }
}

Answered By - plplmax