Why I received "Operator is not overloaded" complie error while using Generic?

[shyakocat]

I feel confused when I'm programming such kind of code.
I use Free Pascal 3.0.2;

Code: Pascal  [Select][+][-]

1. Uses GUtil;
2. Type
3.  Rana=Record x,y:Longint End;
4.  
5. Operator <(const a,b:Rana)c:Boolean;  //hint:const or not doesn't matter
6. Begin Exit(a.x<b.x) End;
7.  
8. Type
9.  RLess=Specialize TLess<Rana>;
10.  
11. Begin
12.  
13. End.
14.  

If I complie codes above.I'll got an {Error: Operator is not overloaded: "Rana" < "Rana" }.Why is that and what should I do to solve this.

[molly]

This contruct is not possible yet, see also operator overloading.

Currently, due to an implementation restriction, it will not work using a global operator..

and

Support for this construct is expected in a future version of Free Pascal.

Use advanced record with a record operator:

Code: Pascal  [Select][+][-]

1. {$MODESWITCH ADVANCEDRECORDS}
2.  
3. Uses
4.   GUtil;
5.  
6. Type
7.   Rana=
8.   Record
9.     x,y:Longint;
10.     class Operator <(const a,b:Rana)c:Boolean;  //hint:const or not doesn't matter
11.   End;
12.  
13. class Operator rana.<(const a,b:Rana)c:Boolean;  //hint:const or not doesn't matter
14. Begin
15.   Exit(a.x<b.x)
16. End;
17.  
18. Type
19.  RLess=Specialize TLess<Rana>;
20.  
21. Begin
22. End.
23.  

[shyakocat]

Thanks a lot.

[Thaddy]

The construct is possible with 3.0.4 and trunk, but there is a limitation in the fgl unit. .
Here is an example using fcl-stl and another generic container type:

Code: Pascal  [Select][+][-]

1. program untitled;
2. {$mode objfpc}{$H+}{$I-}
3. uses glinkedlist;//generics.collections; is also possible from trunk
4. type
5.   TVec2 = object
6.   end;
7.   TVec2List = specialize TlinkedList < TVec2 >; //generics.collections: Tlist<>
8.  
9. operator = (const A:Tvec2,TVec2 ): Boolean;
10. begin
11.   Result:= True;
12. end;
13. begin
14. end.
15.  

The language supports it since 3.0.4. for anything, records, classes, objects, simple types... Docs are outdated, I think, unless it missed the 3.0.4 release...
Anyway: with trunk even more is possible.