在Delphi中：如何在不使用参数的情况下找到递归深度？

Question

When I create recursive methods, I often include a Depth-parameter, especially when I need some sort of bailout mechanism. The code will usually be something like this

procedure Recurse(<Params>; aDepth : integer = 0);
begin
  if aDepth > SomeLimit then
  begin
    //Tidy up, return best result found>
    exit;
  end;

  <stuff>

  if <Condition> then
    Recurse(<Params>; aDepth+1)
  else 
  begin 
    //Tidy up, return result of endnode>
  end;
end;

And I call it without the Depth-parameter

Recurse(<Params>);

Is there another way to easily find the depth?

Answer 1

If you had a way to walk the stack and see how many times your function's entry point was in there, I suppose you could do it that way. But then you'd notice that your aDepth parameter was right there too, and you'd realize that aDepth is just easier and much less trouble than snooping the stack. IMO, the simple solution is best here, it's portable and future-proof, unlike whatever stack snooping solution you could invent.
So yes, there are other ways, but your original solution is best, IMO.

Answer 2

Declare a typed constant inside your procedure. Make sure you set the compile option to allow changes in constants.

procedure Recurse;
const
  aDepth : integer = 0;
begin
  aDepth := aDepth + 1;

  try
    if aDepth > SomeLimit then
    begin
      //Tidy up, return best result found>
      exit;
    end;

    <stuff>

    if <Condition> then
      Recurse
    else 
    begin 
      //Tidy up, return result of endnode>
    end;
  finally
    aDepth := aDepth - 1;
  end;
end;

Answer 3

Have a global variable that would count recursion? Otherwise no - recursion is just calling some method with some parameters.

Answer 4

In C++ I am able to do this

class recursion_guard
{
public:
    recursion_guard() { depth_count++; }
    ~recursion_guard() { depth_count--; }
    static int depth_count;
};
int recursion_guard::depth_count = 0;
void recurse(recursion_guard a = recursion_guard())
{
    if(recursion_guard::depth_count > 100)
        return;
    recurse();
}

but since objects in Object Pascal are always allocated on the heap, I wonder if it is possible to use instead String with default argument and access somehow its reference count

const 
    MyRecursionGuardConstString: string = "whatever";
procedure Recurse(RecursionGuard: string = MyRecursionGuardConstString) 
begin
    if GetRefCount(MyRecursionGuardConstString) > 100 then //o_o
        exit;
    end;
    Recurse;
end;

Answer 5

type
  TMyRecursion = class
  private
    nDepth: integer;
  public
    constructor Create;
    procedure Recursion(...)
  end;

In constructor you must initialize nDepth, of course.