Dear Michael,
thank you for the explanation. I understand that the helper overwrites the
original constructor. But...
I have defined "type TSomething = type TVec3f" (note the second "type"). So
from my perspective, I'd assume that the TSomethingHelper doesn't apply to
TVec3f at all because TSomething is defined as a new type, not only an alias
for TVec3f.
----- Original Message -----
From: Michael Van Canneyt via fpc-pascal <fpc-pascal@lists.freepascal.org>
To: Thomas Kurz via fpc-pascal <fpc-pascal@lists.freepascal.org>
Sent: Tuesday, May 9, 2023, 23:55:47
Subject: [fpc-pascal] Record Constructors which differ in parameter lists
On Tue, 9 May 2023, Thomas Kurz via fpc-pascal wrote:
> Hello,
> let's take the following example:
> program Project1;
> {$MODE OBJFPC}
> {$MODESWITCH ADVANCEDRECORDS}
> {$MODESWITCH TYPEHELPERS}
> type TVec3f = record
> x, y, z: Double;
> constructor Create (a1, a2, a3: Double);
> end;
> type TSomething = type TVec3f;
> type TSomethingHelper = type helper for TSomething
> constructor Create (a1, a2: Double);
> end;
> constructor TVec3f.Create (a1, a2, a3: Double);
> begin
> Self.x := a1;
> Self.y := a2;
> Self.z := a3;
> end;
> constructor TSomethingHelper.Create (a1, a2: Double);
> begin
> Self.x := a1;
> Self.y := a2;
> Self.z := 1 - a1 - a2;
> end;
> var f: TVec3f;
> begin
> f := TVec3f.Create (0.0, 0.0, 0.0); // <-- error here
> end.
> I get the error:
> project1.lpr(35,37) Error: Wrong number of parameters specified for call to
> "Create"
> project1.lpr(25,30) Error: Found declaration: constructor
> Create(Double;Double);
> So, obviously, FPC tries to apply the helper of TSomething (which should be
> decoupled from TVec3f because of the "type TVec3f" declaration) to TVec3f
> which hasn't defined any constructor with 2 parameters.
> Is this intended behavior or should I report it as a bug?
This is intended behaviour since declarations in helpers always take
precedence over the methods in the class/record.
Try to add overload; to the constructor in the helper. This is a hint to the
compiler that it should look for other methods.
Michael.
_______________________________________________
fpc-pascal maillist - fpc-pascal@lists.freepascal.org
https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
_______________________________________________
fpc-pascal maillist - fpc-pascal@lists.freepascal.org
https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
