Re: [fpc-pascal] Caller agnostic procedure variables

[Michael Van Canneyt via fpc-pascal]

On Tue, 15 Feb 2022, Ryan Joseph via fpc-pascal wrote:



On Feb 15, 2022, at 2:09 PM, Michael Van Canneyt via fpc-pascal 
<fpc-pascal@lists.freepascal.org> wrote:

I've answered this question before:

The "Reference to procedure" that will be part of anonymous functionswill do 
this for you.

I'm sorry I forgot! This thing keeps coming up for me and driving me nuts but I 
knew I asked in passing before.

So "reference to procedure" are going to be the new standard?

I don't know what you mean by 'new standard', but a new type, yes.

We're not going to change all procedural types to this new type, if that's
what you have in mind.

To extend
my example it would look like this?  I please remind me, is there a
closure involved which is capturing state and adding overhead?

There is not necessarily a closure; only if you use an anonymous function.


I'm curious what this type actually is also, maybe a dispatch table which wraps 
the existing types or is it something totally new?

I will leave it to the compiler people to answer this, because I don't know
the low-level details.


====================

type
 TMyAction = reference to procedure;

procedure DoThis(action: TMyAction);
 begin
   action();
 end;

Yes. The following compiles and runs in delphi:

program procdemo;

{$APPTYPE CONSOLE}

{$R *.res}

Type
  TProc = reference to procedure;

  TMyObject = Class
    Procedure DoA;
    Procedure DoTest(aTest : TProc);
    Procedure Demo;
  End;

Procedure DoPlain;

begin
  Writeln('Plain');
end;

{ TMyObject }

procedure TMyObject.Demo;
begin
  DoTest(DoA);
  DoTest(DoPlain);
  DoTest(Procedure
   begin
     Writeln('anonymous');
   end);
end;

procedure TMyObject.DoA;
begin
  Writeln(ClassName,': A');
end;

procedure TMyObject.DoTest(aTest: TProc);
begin
  aTest;
end;

begin
  With TMyObject.Create do
    try
      Demo;
    finally
      Free;
    end;
end.

I requested that this:

procedure TMyObject.Demo;

  Procedure DoSub;
  begin
    Writeln('Sub');
  end;

begin
  DoTest(DoSub);
end;

would also work. It does not work in Delphi, but Pas2js already supports that. 
I think it results in more readable code - the whole anonymous stuff doesn't really work for me...

Michael.
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