[Lazarus] Error: Generics without specialization cannot be used as a type for a variable

[Peter Williams]

Hi All,

From: pewilliams2010 at live.com
To: lazarus at lists.lazarus.freepascal.org
Date: Mon, 9 May 2011 16:32:04 +1000
Subject: Re: [Lazarus] Error: Generics without specialization cannot be used as a type for a variable








Hi Sven & all,

> Date: Fri, 6 May 2011 22:06:55 +0200
> From: pascaldragon at googlemail.com
> To: lazarus at lists.lazarus.freepascal.org
> Subject: Re: [Lazarus] Error: Generics without specialization cannot be used as a type for a variable
> 
> On 06.05.2011 17:58, Peter Williams wrote:
> > Hi,
> >
> > Options changed, recompiling clean with -B
> > Hint: Start of reading config file /etc/fpc.cfg
> > Hint: End of reading config file /etc/fpc.cfg
> > Free Pascal Compiler version 2.4.2-0 [2010/11/11] for i386
> > Copyright (c) 1993-2010 by Florian Klaempfl
> > Target OS: Linux for i386
> > Compiling island_maker.lpr
> > Compiling unit1.pas
> > unit1.pas(144,19) Error: Generics without specialization cannot be used
> > as a type for a variable
> > unit1.pas(152,1) Fatal: There were 1 errors compiling module, stopping
> >
> > http://62.166.198.202/bug_view_advanced_page.php?bug_id=18101
> >
> > (0043710)
> > Florian Klämpfl (administrator)
> > 2010-11-29 10:47
> >
> > 	Please use always the latest release compiler (2.4.2) as starting
> > compiler to build a new fpc.
> >
> >
> > NB - I am using FPC 2.4.2.
> >
> > type
> > Terrain_type = (Land, Sea);
> >
> > exit_type = array[ directions ] of integer;
> >
> > description_type = array[1..2] of string;
> >
> > Tmap_detail = Object
> > FTerrain : Terrain_type;
> > FTerrain_char : char;
> > Fdescription : description_type;
> > Fx, Fy, Flocation_number : integer;
> > Fexits : exit_type;
> > end;
> >
> > // The Island class definition
> > Generic TIsland<T> = class
> > Items : array of Tmap_detail;
> > public
> > constructor Create(AList: TList);: [Lazarus] dtm_maker project compile
> > errors with TList code.
> > procedure Add( Value : Tmap_detail );
> > end;
> > var
> > Form1: TForm1;
> > Island : TIsland; // line 144
> >
> > Unit1.pas >>> http://pastebin.com/wuEft4Kb
> 
> Why do you declare TIsland as a generic if you don't use the type "T" 
> anywhere?
> 
> Nevertheless, you need to declare a specialized type of a generic, so 
> you're able to use it.
> 
> Example:
> 
> type
>    TIntegerIsland = specialize TIsland<Integer>;
> 
> var
>    Island: TIntegerIsland;
> (...)
Okay, except that Island is not meant to be an integer. See here:
line 88Tmap_detail = Object                 FTerrain : Terrain_type;                 FTerrain_char : char;                 Fdescription : description_type;                 Fx, Fy, Flocation_number : integer;                 Fexits : exit_type;               end;   // The Island class definition  Generic TIsland<T> = class      Items : array of Tmap_detail;    public    constructor Create(AList: TList);    procedure Add( Value : Tmap_detail );  end;
>So, as you can see, I am trying to define a Generic (or possibly a Specialize) of type: an array of Tmap_detail. How do I correctly define this???
>The reason why I am choosing a Generic or Specialize is so that I have accept to the "Sort" procedure of TList. I am not sure if I am doing this correctly.
>Best Regards,>Peter
I have (though all of these posts) been trying to follow the instructions for GENERICS on this page:
http://wiki.lazarus.freepascal.org/Generics
This page makes no reference to SPECIALIZE keyword.
Can someone please provide an example of using a TList and an object (as in my code) so that I had access to a custom Tlist with the Sort procedure... which is really my reason for needing this.
Best Regards,Peter

> 
>> Regards,
>> Sven
> 
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