Hi All,

How can I use operator overloading? ?I know the syntax, but it simply does not compile... ?My situation is:

1. I wrote a TTreap generic class, which is a binary tree.
2. TTreap defines a Compare() with involves < and > operation on its keys.
3. I try to specialize it with the following:

===================================================
interface
TPainterManager = class(specialize TTreap<TPainter, Integer>)
public
? ? class operator < (p1, p2: TPainter) b: Boolean; <-- method1
end;

operator < (p1, p2: TPainter) b: Boolean; <-- method2

implementation
..
===================================================

but neither method1 nor method2 compiles.

What is the correct way to write operator overload routines?

Thanks,
Shannon ?I?
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FPC operator overloading doesn't work inside classes, it must be declared globally, so method2 should work. What error do you get? What FPC version do you use?

From: xrfang
Sent: Sunday, February 24, 2013 7:31 AM
To:
Subject: [Lazarus] operator overloading

operator < (p1, p2: TPainter) b: Boolean; <?method2

Close, but no cigar...

operator < (p1, p2: TPainter): Boolean;

--------------------------------------------------------------------------------

Both variants will work. The variant with "b: Boolean" was originally introduced for the non-Object-Pascal modes (fpc, tp), because there you only have the name of the procedure/function as a result variable and as operators don't have names (in that sense) you can specify the name of the result variable. It works in the Object Pascal modes (delphi, objfpc) however as well.

Regards,
Sven

I will test again tomorrow to find out what's wrong with my code. ?For now, one more queston:

I noticed that generics does not work without {$mode objfpc}. ?I wonder what is the default mode without $mode? Why objfpc is not the default mode?

? ?, 2? 24, 2013 at 11:00 ???Sven Barth ???

Both variants will work. The variant with "b: Boolean" was originally introduced for the non-Object-Pascal modes (fpc, tp), because there you only have the name of the procedure/function as a result variable and as operators don't have names (in that sense) you can specify the name of the result variable. It works in the Object Pascal modes (delphi, objfpc) however as well.

Regards,
Sven

There is only one way how you can solve this: the type TPainter MUST be a record and there you can define the operator using "class operator <" and "class operator >" (in mode ObjFPC you need to use {$modeswitch advancedrecords} as well).

Maybe one can think about allowing operators in other structured types (classes, objects, interfaces) as well...

Regards,
Sven

Thanks for the Heads Up Sven, you learn something new everyday.

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The default mode is "fpc" and it will stay the default mode because of backwards compatibility. The difference between the two modes is that "fpc" is a bit more like "tp" (no classes, only objects) but with additional features. Generics will work for objects, records, arrays and procedural types in that mode.

Regards,
Sven

I confirm that it does not work. ?Test program below, and the class source is attached.

==Test Program===================

program test;
{$mode objfpc}{$H+}
uses
? Classes, treap;
type
? TSLCounter = specialize TTreap<TStringList, Integer>;
operator <(sl1, sl2: TStringList): Boolean;
begin
? Result := sl1.Text < sl2.Text;
end;
begin
end.

==Error Message==================
Options changed, recompiling clean with -B
/home/xrfang/git/fpcollection/src/units/treap.pas(216,10) Error: Operator is not overloaded: "TStringList" < "TStringList" /home/xrfang/git/fpcollection/src/units/treap.pas(218,15) Error: Operator is not overloaded: "TStringList" > "TStringList" test.lpr(19) Fatal: There were 2 errors compiling module, stopping =================================

i.e. whether the operator overloading is defined or not, error message is same.

Thanks.

? ?, 2? 24, 2013 at 4:21 ???leledumbo ???
FPC operator overloading doesn't work inside classes, it must be declared globally, so method2 should work. What error do you get? What FPC version do you use?