Need help on some C# to Delphi Conversion

[Adz Baywes 0]

I am currently converting some C# code to Delphi and came across some methods that I am not sure on how to properly translate. The C# goes like this:

public class Test
{
	public string TestMe { get; set; }
	public string Category(string cat)
	{
		...
	}
}

...

public class DoTest
{
	public async Task<Test> Meth(string message)
	{
		return await Category(message);
	}
}

The async Task<T> Meth() function is where I'm lost

type
  TTest = class
  private
    FTestMe: string;
	FCategory: string;
  public
    function TestMe: string read FTestMe write FTestMe
	function Category: string read FCategory write FCategory
  end;
  
...

type
  TDoTest = class
  public
    function Meth(AMessage: string): Test
  end;  
  
implementation

function TDoTest.Meth(AMessage: string): Test
var
  MyTask: ITask;
begin
  MyTask := TTask.Create(
    procedure
	begin
	  ...
	end
  );
  MyTask.Start;
end;

Can this be done with PPL and is my declaration/implementation of the function even correct?

[Vincent Parrett 657]

There isn't really a 1 for 1 conversion here - the Delphi language/ppl does not have any async/await constructs . 

 

So because of that your translation isn't correct. That said, your c# example isn't valid either. 

 

Your TDoTest.Meth doesn't actually return anything so that's a problem there. 

 

So you are left with a few options. Deal with it yourself. which as you have found is not easy (even with the PPL) - or find another library that could handle it. If you are doing this for windows only, OmniThreadLibrary is an option but has a fairly steep learning curve (worth it if you need to do complex threading stuff). For simple code, I wrote a wrapper over Omni (VSoft.Awaitable) which provides a poor mans version of async/await (omni does have this too, but it's missing a few features like cancellation and returning values).

 

function TDoTest.Meth(AMessage: string): IAwaitable<Test>
begin
//configure our async call and return the IAwaitable<string>
  result := TAsync.Configure<Test>(
        function(const cancelToken : ICancellationToken) : Test
        begin
            //.... do some long running thing
            result := TTest.Create
        end, token);	

end;

//calling code

procedure TAnotherClass.DoSomething;
var
  doTest : TDoTest;
begin
  doTest : TDoTest.Create;
	
  //this will not block.
  doTest.Meth('the message', FTokenSource.Token)
     // optional
     .OnException( 
        procedure (const e : Exception)
        begin
          //handle the exception - runs in calling thread
        end)
    // optional
    .OnCancellation(
        procedure
        begin
          // call was cancelled - do any cleanup here
          // runs in calling thread
        end)
	// required, the call to Await actually fires off the task
    .Await(
        procedure (const value : TTest)
        begin
            //runs in the calling thread.
            Label1.Caption := value.TestMe;
        end);

end;

The FTokenSource above is an ICancellationTokenSource - VSoft.Awaitable depends on VSoft.CancellationToken - in VSoftAwaitable it maps over Omnithread's cancellation token - delphi doesn't have one in the rtl or PPL (a glaring omission imho). 

 

It's hard to give a definative example with the invalid c# example though. 

 

BTW, to understand what async/await actually does in C#, this page sums it up quite nicely.

Edited September 20, 2021 by Vincent Parrett
typo

[Adz Baywes 0]

Hi Vincent, thanks for taking the time answering my inquiry. I was also looking at your CancellationToken yesterday as it may be needed on my project, the C# code does use it. The example and explanation you have provided is sufficient for now. I will have to do some more research and read up on the link you have provided. Will be posting if anything comes up. Thanks again!