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Class properties

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Each class can have its own properties. A property looks out like a variable in object, but user doesn't have direct access to variable. Input/output can be redirected trough a procedure or function.

type TTest = class
       private
            propX : integer;
            propY : integer;
       public
         property x : integer read x write x;
         property y : integer read y write y;
       end;
var Test : TTest;
begin
  Test.x := 1;
  Test.y := 2;
  writeln(Test.x);
  writeln(Test.y);
end.

This example shows:

1
2

This is easy example. values of properties are stored directly to variables. But there is one big advantage redirecting data trough function.

type TTest = class
       private
            propX : integer;
            propY : integer;
         function ReadInt (index : cardinal) : integer;
         procedure WriteInt (index : cardinal; value : integer);
       public
         property x : integer index 1 read ReadInt write WriteInt;
         property x : integer index 2 read ReadInt write WriteInt;
       end;
function TTest.ReadInt (index : cardinal) : integer;
begin
  case index of
       1 : ReadInt:=propX;
       2 : ReadInt:=propY;
  end;
end;
procedure TTest.WriteInt (index : cardinal; value : integer);
begin
  case index of
       1 : propX:=value;
       2 : propY:=value;
  end;
end;
var Test : TTest;
begin
  Test.x := 1;
  Test.y := 2;
  writeln(Test.x);
  writeln(Test.y);
end.

Result of this example is the same as below. But procedure can control the value that is passed to the variable and verify it.
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