a missing functionality that could save me a lot of time today

-
a missing functionality that could save me a lot of time today
 TypeOf(typed_variable) insteed of TypeOf(TVariableType)

the purpose is to use RTTI to load a complex API like this:

var
  Sample: record
    getText: function: PChar; stdcall;
    setText: procedure(Value: PChar); stdcall;
  end;

Sample.getText := GetProcAddress(dll, 'Sample_getText');
Sample.setText := GetProcAddress(dll, 'Sample_setText');

Comments

  1. Jeroen Wiert PluimersOctober 20, 2014 at 11:27 AM

    You might be able to use generics for that.  

    function Foo(const param: T);
    begin
      if TypeOf(T) ... then
    end;

    ReplyDelete
  2. Paul TOTHOctober 20, 2014 at 12:25 PM

    Well, and then, how to use for the "Sample" record ?

    No I have to split the declaration

    type
      Sample = record
      ...
      end;

    var
      SampleAPI: Sample;

      LoadAPI(SampleAPI, TypeOf(Sample));

    ReplyDelete
  3. Jeroen Wiert PluimersOctober 20, 2014 at 1:27 PM

    I now see what you mean. That's what you have BPL files for. Then te compiler takes care of everything.

    ReplyDelete
  4. Asbjørn HeidOctober 20, 2014 at 4:58 PM

    If Delphi had some decent type inference, Generics would do the trick. I still prefer the generics route as it is at least somewhat safer, as it'll complain if the type parameter and the variable type do not match.

    http://pastie.org/9664064

    ReplyDelete
  5. Paul TOTHOctober 21, 2014 at 1:29 AM

    Nice code, it's almost what I've done, but as far as I know, the use of a generic duplicate the loader routine for each API...but it's exactly the same code ! (except  line 41 on the call to TypeInfo)

    I don't use Generic for that reason, I mean a TList could be nice to let the COMPILER check for correct type use, but a TList of TButton uses exactly the same code as a TList of TAnyThingElse, there's no reason to duplicate it.

    ReplyDelete
  6. Asbjørn HeidOctober 21, 2014 at 1:59 AM

    Paul TOTH Well, yeah, personally I tend to accept the tradeoff in terms of increased productivity. But I agree it would be nice we had COMDAT folding in Delphi too.

    ReplyDelete
  7. Asbjørn HeidOctober 21, 2014 at 2:02 AM

    Paul TOTH And TList is *not* the same as TList, for an arbitrary TFoo. It may be the same, but it could also be different. If TFoo is a record type for example, the code will be different.

    ReplyDelete
  8. Paul TOTHOctober 21, 2014 at 2:12 AM

    Yes, that's what Constraints  are for ;)

    ReplyDelete
  9. Asbjørn HeidOctober 21, 2014 at 3:11 AM

    Paul TOTH Right, but then we're back to the missing COMDAT folding. Which I agree is sorely missing.

    ReplyDelete
  10. Paul TOTHOctober 24, 2014 at 1:42 PM

    I have a problem with Generic

    type
      TListAPI = record
        function getItem: T; stdcall;
       function nextItem: T;
      end;

    // specific THandle for 2 APIs
     HItem1 = type THandle;
      HItem2= type THandle;

    var
      API1: TListAPI;
      API2: TListAPI;

    function TListAPI.nextItem: T;
    begin
      result := getItem;
      if Result = 0 then // <<-- do not compile :/
       raise Exception.Create('item is null');
    end;

    ReplyDelete
  11. Paul TOTHOctober 24, 2014 at 1:53 PM

    AAAAHHHHAHAHAHAHAHA  !!!!

    procedure TListAPI.Check(Value: T);
    var
      HValue: THandle absolute Value;
    begin
      if HValue = 0 then ...
    end;

    and then :
    [dcc32 Erreur fatale] TestAPI.pas(3951): F2084 Erreur interne : AV06D82806-R00000000-0

    ReplyDelete
  12. Paul TOTHNovember 1, 2014 at 10:31 AM

    THandle is not a valid constraint :(

    ReplyDelete

Post a Comment