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Cannot convert void to Task, when passing a delegate to a method with generic

August 15, 2023

I have the following method that accepts a delegate:

public async Task<T> ExecuteWithRetryAsync<T>(Func<Task<T>> action)
        {
            try
            {
                return await _retryPolicy.ExecuteAsync(async () =>
                {
                    return await action();
                });
            }
            catch (HttpRequestException)
            {
                return default(T);
                //log this to queue
            }
        }

Normally I call it this way and it works fine:

  var saleCheckResult = await ExecuteWithRetryAsync(async () => await _client.CheckSaleAsync(SaleId));

This is the delegate I am passing:

  public virtual System.Threading.Tasks.Task<SaleCheckResult> CheckSaleAsync(string saleId)
    {
        return CheckSaleAsync(saleId, System.Threading.CancellationToken.None);
    }

Here is the problem, I have the following method I want to pass to the Execute with retry as a delegate:

 public virtual System.Threading.Tasks.Task DisableMachineAsync(string machineId)
    {
        return DisableMachineAsync(machineId, System.Threading.CancellationToken.None);
    }

I am using the same logic to call it:

await ExecuteWithRetryAsync(async () => await _client.DisableMachineAsync(machineId));

I get the following error " type arguments for method cannot be inferred from usage try to specify arguments explicitly", I understand I should specify arguments, so I tried this since the delegate returns a Task

  await ExecuteWithRetryAsync<Task>(async () => await _client.DisableMachineAsync(machineId))

Now I get an error cannot implicitly convert void to Task, something I dont understand I cannot use void as a type argument so how can I make sure I pass the correct delegate. Why is it telling me that it wants to convert void to Task, the delegate is returning Task and also the ExecuteWithRetry, how can I make this compile. I found a similar post here but thats a bit different issue Cannot implicitly convert type 'void' to 'System.Threading.Tasks.Task'

>Solution :

You can create an overload which will accept Func<Task>:

async Task ExecuteWithRetryAsync(Func<Task> action)
{
    try
    {
        await _retryPolicy.ExecuteAsync(async () =>
        {
             await action();
        });
    }
    catch (HttpRequestException)
    {
        //log this to queue
    }
}

And let compiler select an overload based on the provided func.