Re: How can I remove dynamic_cast and if statements from this code snippet?

On Nov 16, 12:03 pm, red floyd<no.spam.h...@its.invalid> wrote:


Red,

Thank you for your reply. I believe you have attempted to solve my
problem by modifying the original shapes to return their "XML
components" as strings.

Unfortunately this is not what I am interested in because it does not
scale to what I really want to do. Instead of writing a long-winded
response that might not come across correctly, allow me to change my
original question to use drawing instead of string writing:

===

Is it possible in C++ to modify "Library B" below to eliminate the
dynamic_cast and switch statements, while at the same time not doing
any of the following:
- Do not use DeviceContext in "Library A"
- Do not put drawing code in "Library A"
- Do not put the concept of drawing into "Library A" including adding
a class Shape::GetPixelsToDraw

My goal is to
a) not put any reference to drawing into Library A
b) not use dynamic_cast or switch/if blocks in Library B

The answer might be something like "use factories" or "use template"
or "this is not possible in c++".

Thank you,

Chris

// Library A
struct Shape { virtual ~Shape() {} };
struct Circle : public Shape { float radius; };
struct Square : public Shape { float edge; };

// Library B

#include<cmath>
struct DeviceContext { void FillPixel(int PixelX, int PixelY) {}; };

class Drawer
{
   static void write(Shape* shape, DeviceContext& Dc)
   {
     if (Circle* circle = dynamic_cast<Circle*>(shape))
     {
       for (float Angle = 0; Angle< 2*3.14156; Angle += 0.1)
       {
         Dc.FillPixel(cos(Angle) * circle->radius, sin(Angle) * circle-


       }
     }
     else if (Square* square = dynamic_cast<Square*>(shape))
     {
       Dc.FillPixel(0, 0);
       Dc.FillPixel(square->edge, 0);
       Dc.FillPixel(square->edge, square->edge);
       Dc.FillPixel(0, square->edge);
     }
   }
};