Are there any advantages in using const parameters with an ordinal type?

Question

I know marking string parameters as const can make a huge performance difference, but what about ordinal types? Do I gain anything by making them const

Answer 1

There's a huge speed improvement using Const with strings:

function test(k: string): string;
begin
  Result := k;
end;

function test2(Const k: string): string;
begin
  Result := k;
end;

function test3(Var k: string): string;
begin
  Result := k;
end;

procedure TForm1.Button1Click(Sender: TObject);
Var a: Integer;
    s,b: string;
    x: Int64;
begin
  s := 'jkdfjklf lkjj3i2ej39ijkl  jkl2eje23 io3je32 e832 eu283 89389e3jio3 j938j 839 d983j9';

  PerfTimerInit;
  for a := 1 to 10000000 do
   b := test(s);
  x := PerfTimerStopMS;
  Memo1.Lines.Add('default: '+x.ToString);

  PerfTimerInit;
  for a := 1 to 10000000 do
   b := test2(s);
  x := PerfTimerStopMS;
  Memo1.Lines.Add('const: '+x.ToString);

  PerfTimerInit;
  for a := 1 to 10000000 do
   b := test3(s);
  x := PerfTimerStopMS;
  Memo1.Lines.Add('var: '+x.ToString);
end;

default: 443 const: 320 var: 325

default: 444 const: 303 var: 310

default: 444 const: 302 var: 305

Same with Integers:

default: 142 const: 13 var: 14

Interestingly though, in 64-bit there seems to be almost no difference with strings (default mode is only a bit slower than Const):

default: 352 const: 313 var: 314