Re: [fpc-devel] case is

[Hairy Pixels via fpc-devel]

> On Mar 24, 2022, at 7:21 AM, Michael Van Canneyt via fpc-devel 
>  wrote:
> 
> I am all for merging the implementation of Ryan, but this is not my domain,
> so one of the compiler people needs to look at it.
> 

FPC badly needs another reviewer or someone with authority otherwise. I’ve been 
waiting for Sven to get cleared up with the closures but this is taking months 
and years and in the mean time the “implicit function specialization” has been 
sitting there for a year already (started it in 2019) and now we have the 
Extended RTTI which is in the pipeline (can they be merged soon?). 

Given that this could take well over a year to get reviewed and merged but at 
least Sven did approve of the idea. If a project has these kinds of delays in 
management it’s probably time to reconsider some things, no?

Regards,
Ryan Joseph

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Re: [fpc-devel] case is

[Hairy Pixels via fpc-devel]

> On Mar 24, 2022, at 8:14 AM, Hairy Pixels  wrote:
> 
> Search for "Case statement for class introspection” and you see can the 
> little discussion we had about a potential speed up and why it wasn’t viable 
> so for now it’s just using a if-else statement with A.ClassType = B.ClassType 
> comparisons. It’s just syntactic sugar at this point but it was trivial to 
> implement and I think it’s much nicer to work with so for me that’s a total 
> win.
> 

I just realized one thing worth changing. So this is how I implemented it, 
essentially it’s a case-of-ClassType, which means the compiler now has: case of 
ordinal, case of string and case of classType.

c := TInterfacedObject.Create;

  case c of
TObject:result := 1;
TInterfacedObject:  result := 2;
TAggregatedObject:  result := 3;
otherwise   result := 4;
  end;

But because I did an implicit “c.ClassType” it wouldn’t be possible to use 
“nil” as a case. Maybe not a big deal because you can capture nil in 
“otherwise” but it’s something to consider.

Regards,
Ryan Joseph

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Re: [fpc-devel] case is

[Hairy Pixels via fpc-devel]

> On Mar 23, 2022, at 10:09 PM, Stefan Glienke via fpc-devel 
>  wrote:
> 
> JEP 420 is hardly a misnomer because it is so much more than just type 
> checking in a switch statement - hence pattern matching.
> You can see in the various examples that you can combine all kinds of boolean 
> expressions - C# has had this for quite a while and they are constantly 
> improving it.


Yes, Swift has some of these patterns like “case something where something.name 
== “John”:” but that’s another feature altogether.I see the reason for this and 
it’s interesting but I don’t think there’s any chance they would allow this in 
FPC so I skipped over it.

Regards,
Ryan Joseph

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Re: [fpc-devel] case is

[Hairy Pixels via fpc-devel]

> On Mar 23, 2022, at 10:35 PM, Mattias Gaertner via fpc-devel 
>  wrote:
> 
> Forget Java. The point is, that its "case" can be more than mere
> syntactic sugar. It could give a nice speed up and the compiler warns
> about unreachable statements.


Search for "Case statement for class introspection” and you see can the little 
discussion we had about a potential speed up and why it wasn’t viable so for 
now it’s just using a if-else statement with A.ClassType = B.ClassType 
comparisons. It’s just syntactic sugar at this point but it was trivial to 
implement and I think it’s much nicer to work with so for me that’s a total win.

Regards,
Ryan Joseph

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[fpc-devel] MacOS/dwarf: Was there any change to how/when relocation info is included.

[Martin Frb via fpc-devel]

It appears with 3.2.2  the address of a global var in dwarf already 
contains the relocation.
Since fpdebug, does not retrieve any relocation info from lldb, it does 
not adjust any addresses.


But with 3.3.1 it seems different.

https://forum.lazarus.freepascal.org/index.php?topic=58822.new#new

The test app has 2 global vars.
They can be inspected if compiled with 3.2.2.

But compile with 3.3.1 and fpdebug send the following to  lldb:
  memory read --force --size 1 --format x --count 4 1008
  memory read --force --size 1 --format x --count 4 1012
Looks like the offset within the exe, without relocation.

Was there an intentional change to introduce this?
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Re: [fpc-devel] case is

[Michael Van Canneyt via fpc-devel]

On Wed, 23 Mar 2022, Mattias Gaertner via fpc-devel wrote:


On Wed, 23 Mar 2022 22:20:38 +0700
Hairy Pixels via fpc-devel  wrote:


[...]
> Did you use multiple "is" or did you check for sorted and use one
> loop? 


No it’s just like a the case of string syntax which checks for
equality with ClassType so the order does matter. Maybe it’s not
exactly like what Java has then.


Forget Java. The point is, that its "case" can be more than mere
syntactic sugar. It could give a nice speed up and the compiler warns
about unreachable statements.


I am all for merging the implementation of Ryan, but this is not my domain,
so one of the compiler people needs to look at it.

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Re: [fpc-devel] case is

[Mattias Gaertner via fpc-devel]

On Wed, 23 Mar 2022 22:20:38 +0700
Hairy Pixels via fpc-devel  wrote:

>[...]
> > Did you use multiple "is" or did you check for sorted and use one
> > loop? 
> 
> No it’s just like a the case of string syntax which checks for
> equality with ClassType so the order does matter. Maybe it’s not
> exactly like what Java has then.

Forget Java. The point is, that its "case" can be more than mere
syntactic sugar. It could give a nice speed up and the compiler warns
about unreachable statements.

Mattias
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Re: [fpc-devel] case is

[Stefan Glienke via fpc-devel]

JEP 420 is hardly a misnomer because it is so much more than just type checking 
in a switch statement - hence pattern matching.
You can see in the various examples that you can combine all kinds of boolean 
expressions - C# has had this for quite a while and they are constantly 
improving it.
That also means that their order is important and the compiler cannot and does 
not do any sanity check.
Here is some nice article about the C# implementation: 
https://www.thomasclaudiushuber.com/2021/02/25/c-9-0-pattern-matching-in-switch-expressions/
Also I see in JEP 420 they thought of introducing variables for the different 
patterns to avoid having to write unnecessary boilerplate code or hardcasts - 
such as this:

static int coverage(Object o) {
return switch (o) {
case String s  -> s.length();
case Integer i -> i;
default -> 0;
};
}

Ah well and using the switch statement as an expression so you get the complete 
package of nice and very expressive code.

> On 23/03/2022 13:44 Mattias Gaertner via fpc-devel 
>  wrote:
> 
>  
> Hi,
> 
> I just stumbled over the new Java feature "Pattern Matching for switch".
> https://openjdk.java.net/jeps/420
> IMO it is a misnomer, but it has some interesting ideas.
> 
> Basically for Pascal it is a case block using the "is" operator.
> Pseudo code:
> 
> procedure Fly(o: TObject);
> begin
>   case o is
> TButton: TButton(o).foo;
> TControl: TControl(o).bar;
> TComponent: TComponent(o).meh;
> nil: Msg;
>   else Run;
>   end;
> end;
> 
> The gain versus "if o is then..." is that the compiler warns if the
> case statements are not sorted and can optimize the checks.
> 
> For example the above code could be converted to:
> 
> procedure Fly(o: TObject);
> var
>   tmp: TClass;
> begin
>   if o<>nil then
>   begin
> tmp:=o.ClassType;
> repeat
>   if tmp=TButton then
>   begin
> TButton(o).foo;
> break;
>   end else if tmp=TControl then
>   begin
> TControl(o).bar;
> break;
>   end else if tmp=TComponent then
>   begin
> TComponent(o).meh;
> break;
>   end;
>   tmp:=tmp.ClassParent;
>   if tmp=nil then
>   begin
> Run;
> break;
>   end;
> until false;
>   end else
> Msg;
> end;
> 
> What do you think?
> 
> 
> Mattias
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Re: [fpc-devel] case is

[Hairy Pixels via fpc-devel]

> On Mar 23, 2022, at 10:13 PM, Mattias Gaertner via fpc-devel 
>  wrote:
> 
>> Lol I just implemented this and made a merge request but I haven’t
>> heard back from anyone yet so it’s just sitting there….
>> 
>> I basically just copied the structure used for “case of string” in
>> that it makes if a big if-else statement.
> 
> Did you use multiple "is" or did you check for sorted and use one loop?
> 

No it’s just like a the case of string syntax which checks for equality with 
ClassType so the order does matter. Maybe it’s not exactly like what Java has 
then.

> 
>> https://gitlab.com/freepascal.org/fpc/source/-/merge_requests/147 
>> 
> 
> "Rebase failed"


Yeah, see my other message.  Not sure how to fix that right now but I’ll try if 
it actually reviewed and accepted.

Regards,
Ryan Joseph

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Re: [fpc-devel] case is

[Mattias Gaertner via fpc-devel]

On Wed, 23 Mar 2022 22:00:05 +0700
Hairy Pixels via fpc-devel  wrote:

> Lol I just implemented this and made a merge request but I haven’t
> heard back from anyone yet so it’s just sitting there….
> 
> I basically just copied the structure used for “case of string” in
> that it makes if a big if-else statement.

Did you use multiple "is" or did you check for sorted and use one loop?

 
> https://gitlab.com/freepascal.org/fpc/source/-/merge_requests/147

"Rebase failed"

Mattias


> 
> > On Mar 23, 2022, at 7:44 PM, Mattias Gaertner via fpc-devel
> >  wrote:
> > 
> > Basically for Pascal it is a case block using the "is" operator.
> > Pseudo code:
> > 
> > procedure Fly(o: TObject);
> > begin
> > case o is
> > TButton: TButton(o).foo;
> > TControl: TControl(o).bar;
> > TComponent: TComponent(o).meh;
> > nil: Msg;
> > else Run;
> > end;
> > end;  
> 
> Regards,
>   Ryan Joseph
> 

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Re: [fpc-devel] case is

[Hairy Pixels via fpc-devel]

I just remembered now I tried to follow the procedure to rebase the branch like 
they wanted but I made a big mess of things (notice how it says 400+ changes). 
I don’t know went wrong but you can see the changes I made in the commit 
history but I’m not sure how to isolate them to make a diff. Dunno, but you can 
still checkout the branch and try it.

> On Mar 23, 2022, at 10:00 PM, Hairy Pixels  wrote:
> 
> https://gitlab.com/freepascal.org/fpc/source/-/merge_requests/147 
> 
Regards,
Ryan Joseph

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Re: [fpc-devel] case is

[Hairy Pixels via fpc-devel]

Lol I just implemented this and made a merge request but I haven’t heard back 
from anyone yet so it’s just sitting there….

I basically just copied the structure used for “case of string” in that it 
makes if a big if-else statement.

https://gitlab.com/freepascal.org/fpc/source/-/merge_requests/147

> On Mar 23, 2022, at 7:44 PM, Mattias Gaertner via fpc-devel 
>  wrote:
> 
> Basically for Pascal it is a case block using the "is" operator.
> Pseudo code:
> 
> procedure Fly(o: TObject);
> begin
> case o is
> TButton: TButton(o).foo;
> TControl: TControl(o).bar;
> TComponent: TComponent(o).meh;
> nil: Msg;
> else Run;
> end;
> end;

Regards,
Ryan Joseph

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[fpc-devel] case is

[Mattias Gaertner via fpc-devel]

Hi,

I just stumbled over the new Java feature "Pattern Matching for switch".
https://openjdk.java.net/jeps/420
IMO it is a misnomer, but it has some interesting ideas.

Basically for Pascal it is a case block using the "is" operator.
Pseudo code:

procedure Fly(o: TObject);
begin
  case o is
TButton: TButton(o).foo;
TControl: TControl(o).bar;
TComponent: TComponent(o).meh;
nil: Msg;
  else Run;
  end;
end;

The gain versus "if o is then..." is that the compiler warns if the
case statements are not sorted and can optimize the checks.

For example the above code could be converted to:

procedure Fly(o: TObject);
var
  tmp: TClass;
begin
  if o<>nil then
  begin
tmp:=o.ClassType;
repeat
  if tmp=TButton then
  begin
TButton(o).foo;
break;
  end else if tmp=TControl then
  begin
TControl(o).bar;
break;
  end else if tmp=TComponent then
  begin
TComponent(o).meh;
break;
  end;
  tmp:=tmp.ClassParent;
  if tmp=nil then
  begin
Run;
break;
  end;
until false;
  end else
Msg;
end;

What do you think?


Mattias
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