import std.stdio;

import std.algorithm;

​

struct Entity

 {

   enum NumSystems = 4;

   struct SystemData

   {

     uint start, length;

   }

   SystemData[NumSystems] systemData;

   @property uint systemBits() const { return systemData[].map!(e =>

 e.length).sum; }

 }

​

int main()

{

 Entity e;

 return e.systemBits();

}