Delphi / FPC parameter passing comparison

ExampleDelphi.pas

program ExampleDelphi;

{$VARPROPSETTER ON}

type
  TRecord = record
  private
    FBool: Boolean;
    function GetBoolOut(out Index: NativeUInt): Boolean;
    function GetBoolVar(var Index: NativeUInt): Boolean;
    procedure SetBoolOut(out Index: NativeUInt; out B: Boolean);
    procedure SetBoolVar(var Index: NativeUInt; var B: Boolean);
    function GetBoolConstRef(const [ref] Index: NativeUInt): Boolean;
    procedure SetBoolConstref(const [ref] Index: NativeUInt; const [ref] B: Boolean);
  public
    property OutBools[out Index: NativeUInt]: Boolean read GetBoolOut write SetBoolOut;
    property VarBools[var Index: NativeUInt]: Boolean read GetBoolVar write SetBoolVar;
    property ConstrefBools[const [ref] Index: NativeUInt]: Boolean read GetBoolConstRef write SetBoolConstref;
  end;

function TRecord.GetBoolOut(out Index: NativeUInt): Boolean;
begin
  Result := Index > 5000;
end;

function TRecord.GetBoolVar(var Index: NativeUInt): Boolean;
begin
  Result := Index > 5000;
end;

procedure TRecord.SetBoolOut(out Index: NativeUInt; out B: Boolean);
begin
  FBool := B;
  B := Index > 5000;
end;

procedure TRecord.SetBoolVar(var Index: NativeUInt; var B: Boolean);
begin
  FBool := B;
  B := Index > 5000;
end;

function TRecord.GetBoolConstRef(const [ref] Index: NativeUInt): Boolean;
begin
  Result := Index > 5000;
end;

procedure TRecord.SetBoolConstref(const [ref] Index: NativeUInt; const [ref] B: Boolean);
begin
  FBool := B and (Index > 5000);
end;

var
  R: TRecord;
  I: NativeUInt = 5000;

begin
  // E2033 Types of actual and formal var parameters must be identical
  WriteLn(R.OutBools[5001]);
  // E2033 Types of actual and formal var parameters must be identical
  R.OutBools[5001] := False;
  // E2033 Types of actual and formal var parameters must be identical
  WriteLn(R.VarBools[5001]);
  // E2033 Types of actual and formal var parameters must be identical
  R.VarBools[5001] := False;
  // Works fine
  WriteLn(R.ConstrefBools[5001]);
  // Works fine
  R.ConstrefBools[5001] := False;
  // Works fine
  WriteLn(R.OutBools[I]);
  // E2036 Variable required
  R.OutBools[I] := True;
  // Works fine
  WriteLn(R.VarBools[I]);
  // E2036 Variable required
  R.VarBools[I] := False;
  // Works fine
  WriteLn(R.ConstrefBools[I]);
  // Works fine
  R.ConstrefBools[I] := True;
end.

ExampleFPC.pas

program ExampleFPC;

{$mode Delphi}
{$VARPROPSETTER ON}

type
  TRecord = record
  private
    FBool: Boolean;
    function GetBoolOut(out Index: NativeUInt): Boolean;
    function GetBoolVar(var Index: NativeUInt): Boolean;
    procedure SetBoolOut(out Index: NativeUInt; out B: Boolean);
    procedure SetBoolVar(var Index: NativeUInt; var B: Boolean);
    function GetBoolConstRef(constref Index: NativeUInt): Boolean;
    procedure SetBoolConstref(constref Index: NativeUInt; constref B: Boolean);
  public
    property OutBools[out Index: NativeUInt]: Boolean read GetBoolOut write SetBoolOut;
    property VarBools[var Index: NativeUInt]: Boolean read GetBoolVar write SetBoolVar;
    property ConstrefBools[constref Index: NativeUInt]: Boolean read GetBoolConstRef write SetBoolConstref;
  end;

function TRecord.GetBoolOut(out Index: NativeUInt): Boolean;
begin
  Result := Index > 5000;
end;

function TRecord.GetBoolVar(var Index: NativeUInt): Boolean;
begin
  Result := Index > 5000;
end;

procedure TRecord.SetBoolOut(out Index: NativeUInt; out B: Boolean);
begin
  FBool := B;
  B := Index > 5000;
end;

procedure TRecord.SetBoolVar(var Index: NativeUInt; var B: Boolean);
begin
  FBool := B;
  B := Index > 5000;
end;

function TRecord.GetBoolConstRef(constref Index: NativeUInt): Boolean;
begin
  Result := Index > 5000;
end;

procedure TRecord.SetBoolConstref(constref Index: NativeUInt; constref B: Boolean);
begin
  FBool := B and (Index > 5000);
end;

var
  R: TRecord;
  I: NativeUInt = 5000;

begin
  // Error: Variable identifier expected
  WriteLn(R.OutBools[5001]);
  // Error: Variable identifier expected
  R.OutBools[5001] := False;
  // Error: Variable identifier expected
  WriteLn(R.VarBools[5001]);
  // Error: Variable identifier expected
  R.VarBools[5001] := False;
  // Works fine
  WriteLn(R.ConstrefBools[5001]);
  // Works fine
  R.ConstrefBools[5001] := False;
  // Works fine
  WriteLn(R.OutBools[I]);
  // Error: Variable identifier expected
  R.OutBools[I] := True;
  // Works fine
  WriteLn(R.VarBools[I]);
  // Error: Variable identifier expected
  R.VarBools[I] := False;
  // Works fine
  WriteLn(R.ConstrefBools[I]);
  // Works fine
  R.ConstrefBools[I] := True;
end.