c# - Why there is compiler error: Cannot convert void to string, where as there is no casting happening

Question

I'm not sure why there is compiler error, Argument 1 Cannot convert 'void' to 'string', where as there is no casting happening. Below code creates a list of methods:

void FunctionList(string srcBucket, List<List<string>> pdfFileList, IAmazonS3 s3client)
{
    List<Action> actions = new List<Action>();
    foreach (var list in pdfFileList)
       list.Add(RenameFilesAsync(srcBucket, list, s3client).Wait()); // Getting error here
}

public async Task RenameFilesAsync(string srcBucket, List<string> pdfFiles, IAmazonS3 s3client)
{
  //Some code here
}

Answer 1

Your signature on RenameFilesAsync returns just a Task, not Task<T>. If you don't specify a type, it will not return a value, so it looks like void.

Here's the link to the async return types: https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/async/async-return-types