Re: [fpc-pascal] Make a distinct pointer type

[Hairy Pixels via fpc-pascal]

I just noticed this still doesn't provide good type safety as MyPtr can be 
assigned an untyped pointer. Are pointers simply not an option here? Maybe we 
need classes for opaque pointer types instead?

type
  _MyPtr = record end;
  MyPtr = ^_MyPtr;
var
  p: Pointer;
  x: MyPtr;
begin
  x := p; // Should be an error!
end;

Regards,
Ryan Joseph

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Re: [fpc-pascal] Make a distinct pointer type

[Sven Barth via fpc-pascal]

Hairy Pixels via fpc-pascal  schrieb am
Do., 1. Juni 2023, 03:16:

>
>
> > On May 31, 2023, at 9:20 PM, Michael Van Canneyt via fpc-pascal <
> fpc-pascal@lists.freepascal.org> wrote:
> >
> > Type aliases are always assignment compatible.
>
> btw, what does the "type" prefix do then? I thought that made them
> non-aliases or distinct types.
>

It only makes a difference for the RTTI as well as overloading.

Regards,
Sven

>
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Re: [fpc-pascal] Make a distinct pointer type

[Hairy Pixels via fpc-pascal]

> On May 31, 2023, at 9:20 PM, Michael Van Canneyt via fpc-pascal 
>  wrote:
> 
> Type aliases are always assignment compatible.

btw, what does the "type" prefix do then? I thought that made them non-aliases 
or distinct types.

Regards,
Ryan Joseph

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Re: [fpc-pascal] Make a distinct pointer type

[Hairy Pixels via fpc-pascal]

I'm trying to make an "opaque pointer" type for a c library so the types are 
just pointers but they should be incompatible. I guess I'll have to make all 
the records.

> On May 31, 2023, at 9:20 PM, Michael Van Canneyt via fpc-pascal 
>  wrote:
> 
> Type aliases are always assignment compatible.
> 
> As far as I know, there is no way to do what you want with just 'pointer'.
> 
> This will give an error:
> 
> Type
>  RA = record end;
>  RB = record end;
>  PA = ^RA;
>  PB = ^RB;
> 

Regards,
Ryan Joseph

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Re: [fpc-pascal] Make a distinct pointer type

[Michael Van Canneyt via fpc-pascal]

On Wed, 31 May 2023, Hairy Pixels via fpc-pascal wrote:


What's the best way to make a pointer type which is distinct so that the following 
snippet would give an error. I thought "type pointer" would do it but it 
doesn't seem to work.

type
 PA = type pointer;
 PB = type pointer;

var
 a: PA;
 b: PB;
begin
 a := b; // should give an error!
end;


Type aliases are always assignment compatible.

As far as I know, there is no way to do what you want with just 'pointer'.

This will give an error:

Type
  RA = record end;
  RB = record end;
  PA = ^RA;
  PB = ^RB;

var
  a: PA;
  b: PB;
begin
  a := b;
end.

Michael.
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[fpc-pascal] Make a distinct pointer type

[Hairy Pixels via fpc-pascal]

What's the best way to make a pointer type which is distinct so that the 
following snippet would give an error. I thought "type pointer" would do it but 
it doesn't seem to work.

type
  PA = type pointer;
  PB = type pointer;

var
  a: PA;
  b: PB;
begin
  a := b; // should give an error!
end;

Regards,
Ryan Joseph

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