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Error: Incompatible types: regular procedure and method pointer

Posted on 2001-06-29
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Last Modified: 2012-06-21
I am getting an error (Incompatible types: regular procedure and method pointer) when using procedural types in the following maner:
TMyClass = class
  private
   function compare(a,b: integer): byte;
   procedure someProcedure;
end; {TMyClass}

procedure TMyClass.someProcedure;
begin
  mySort(compare);
end;

I have a unit called sort...

unit sort;
type
  compFunc = function (a,b: integer) : byte;

procedure mysort(compare: compFunc);
begin
  ...
end;

I can't figure out why I am getting this error message.
Thanks in advance
jeco
0
Comment
Question by:jeco
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3 Comments
 
LVL 9

Expert Comment

by:ITugay
ID: 6238318
Hi jeco,

it declared as function (a,b: Integer): byte  "of object".

you should declare
type
  compFunc = function (a,b: integer) : byte; of object;
and assign it not for standalone function, but for object method.

another way to pass address of function as parameter

type
  TMyClass = ...
  ...
   function compare(Proc: CompFunction);
  end;


function TMyClass.Compare(Proc: CompFunction);
begin
   if Proc(A, B) = 0 ...
....

-----
Igor.
0
 
LVL 3

Accepted Solution

by:
alzv earned 300 total points
ID: 6238325
You receive such message because you are trying to pass a method pointer as a parameter. But your procedure can only retrieve an entry point of regular function not a class method. If you want to pass a method into your procedure you need to modify CompFunc type declaration like this:

type
  CompFunc = function (a,b: integer) : byte of object;

Or if you want to pass both types of procedures (regular and methods) you need to overload your MySort procedure like this:

type
  CompFunc = function (a,b: integer) : byte;
  CompFuncMethod = function (a,b: integer) : byte of object;

procedure MySort(Compare: CompFunc); overload;
procedure MySort(Compare: CompFuncMethod); overload;

Best regards,
Alexey Zverev.
0
 

Author Comment

by:jeco
ID: 6239262
Thanks igor and Alexey for your answers. Both answers worked but since I ended up using overload procedures I will give the points to Alex
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