Graeme Geldenhuys
2008-09-18 07:08:04 UTC
Hi,
I was following a discussion in the delphi.non-technical newsgroup.
They raised an issue about distinct types. I tried the following
example under FPC and unexpectedly, FPC doesn't raise any errors!
If you declare a distinct type as follows:
type TMyInteger = type Integer;
The type TMyInteger <> Integer so you are not supposed to be allowed
to assign one to the other. Yet you can. See the following program.
----------------------[ test1.pas ]--------------------------
program test1;
{$mode objfpc}{$H+}
uses
Classes, SysUtils;
type
Angle = type Double;
Length = type Double;
function AngleToLength(var a: Angle):Length; { Note the var parameter }
begin
result := a;
end;
function AngleToLength2(a: Angle):Length; { Here is NO var parameter }
begin
result := a;
end;
procedure Test;
var
a: Angle;
l: Length;
d: Double;
begin
d := Now;
a := d;
l := a; // Should this have failed ????
{ FPC raises no errors, but at least Delphi raises an error wit the
var parameter type. }
a := AngleToLength(l); // This should definitely have failed!!
a := AngleToLength2(l); // Should this fail too?
end;
begin
Test;
end.
--------------------------[ end ]-----------------------------
The program was compiled with FPC 2.2.3:
fpc test1.pas
./test1
Regards,
- Graeme -
_______________________________________________
fpGUI - a cross-platform Free Pascal GUI toolkit
http://opensoft.homeip.net/fpgui/
I was following a discussion in the delphi.non-technical newsgroup.
They raised an issue about distinct types. I tried the following
example under FPC and unexpectedly, FPC doesn't raise any errors!
If you declare a distinct type as follows:
type TMyInteger = type Integer;
The type TMyInteger <> Integer so you are not supposed to be allowed
to assign one to the other. Yet you can. See the following program.
----------------------[ test1.pas ]--------------------------
program test1;
{$mode objfpc}{$H+}
uses
Classes, SysUtils;
type
Angle = type Double;
Length = type Double;
function AngleToLength(var a: Angle):Length; { Note the var parameter }
begin
result := a;
end;
function AngleToLength2(a: Angle):Length; { Here is NO var parameter }
begin
result := a;
end;
procedure Test;
var
a: Angle;
l: Length;
d: Double;
begin
d := Now;
a := d;
l := a; // Should this have failed ????
{ FPC raises no errors, but at least Delphi raises an error wit the
var parameter type. }
a := AngleToLength(l); // This should definitely have failed!!
a := AngleToLength2(l); // Should this fail too?
end;
begin
Test;
end.
--------------------------[ end ]-----------------------------
The program was compiled with FPC 2.2.3:
fpc test1.pas
./test1
Regards,
- Graeme -
_______________________________________________
fpGUI - a cross-platform Free Pascal GUI toolkit
http://opensoft.homeip.net/fpgui/