C++/CX Metro Windows - create_task implementation prevents using variable not defined in that scope - windows

Question

I am trying to define Uri^ outside of the implementation of create_task. In java, if you have an asynchronous task adding the final modifier would allow you to use that variable (with final modifier) inside the asynchronous code.
How can I use Uri^ source from the below code inside the asynchronous code?
void addDownload(Uri^ source, StorageFolder^ destinationFolder, String^ fileName) {
boolean requestUnconstrainedDownload = false;
IAsyncOperation<StorageFile^>^ asyncOperationStorageFile = destinationFolder->CreateFileAsync(fileName, CreationCollisionOption::GenerateUniqueName);
auto createStorageFileTask = create_task(asyncOperationStorageFile);
createStorageFileTask.then([] (StorageFile^ destinationFile) {
BackgroundDownloader^ downloader = ref new BackgroundDownloader();
DownloadOperation^ downloadOperation = downloader->CreateDownload(source, destinationFile);
downloadOperation->Priority = BackgroundTransferPriority::Default;
HandleDownloadAsync(downloadOperation, true);
});
}

Answer 1

Just capture the variable source in the lambda so it can be accessed in the lambda body of the task:
void addDownload(Uri^ source, StorageFolder^ destinationFolder, String^ fileName) {
boolean requestUnconstrainedDownload = false;
IAsyncOperation<StorageFile^>^ asyncOperationStorageFile = destinationFolder->CreateFileAsync(fileName, CreationCollisionOption::GenerateUniqueName);
auto createStorageFileTask = create_task(asyncOperationStorageFile);
createStorageFileTask.then([source] (StorageFile^ destinationFile) {
BackgroundDownloader^ downloader = ref new BackgroundDownloader();
DownloadOperation^ downloadOperation = downloader->CreateDownload(source, destinationFile);
downloadOperation->Priority = BackgroundTransferPriority::Default;
HandleDownloadAsync(downloadOperation, true);
});
}