Converting TStack code from Delphi to Lazarus

Question

In Delphi I have the following code, and all works well:

var
  StackOptions:TStack<String>;
  s:string;
  bfisio:boolean;
begin
  StackOptions:=TStack<String>.Create;
  //some pushs here 
  for s in StackOptions do begin
    dosomething;
  end;
end;

In Lazarus I can do this:

uses
  ..., gstack;

type
  TStringStack = specialize TStack<String>;

var
  StackOptions: TStringStack;
  s:string;
begin
  //But this code doesn;t compile
  StackOptions := TStringStack.Create;
  //some pushs here 
  for s in StackOptions do begin // <-- Error 
    dosomething;
  end;
end;

I get the next error in Lazarus:

Compile Project, Target: TicketLaz.exe: Exit code 1, Errors: 1
umain.pas(263,12) Error: Cannot find an enumerator for the type "TStack$1$crcAC3AF268"

How could I loop the Stack and search for a value with Lazarus without removing items from Stack?

Answer 1

FPC's stack is backed by a TVector.
The TVector has an enumerator.

You can easily add a class helper like so:
Quick and dirty code.

type
  TStringStack = specialize TStack<String>;

 type

   { TStackHelper }

   TVectorEnumerator = specialize TVector<string>.TVectorEnumerator;

   TStackHelper = class helper for TStringStack
     function GetEnumerator: TVectorEnumerator;
   end;

{ TStackHelper }

function TStackHelper.GetEnumerator: TVectorEnumerator;
begin
  Result:= FData.GetEnumerator;
end;

I really don't see why a stack is not supposed to have an iterator.
Even in assembly you can simply do mov reg,[esp-04].
This puritanical approach to data-structures helps no-one

All this is complicated by the fact that TStack is generic.
I know FPC allows generic class helpers, but I'm not sure how to make the solution work for all TStack<T>

Another approach would be to simply edit gstack.pas to expose the iterator.