Raw space (no optimisation, no grid, no quadtree, no ...) every particles are check against every particles (inter Particles and intra Particles group) and check against every Segment

class Space_XY0 implements Space{

 final List<Particles> _particlesS = new List();
 final List<Segment> _segments = new List();
 final Checker checker;
 final Resolver resolver;
 final Vector4 _scol = new Vector4.zero();

 Space_XY0(this.checker, this.resolver);

 void reset() {
   _particlesS.clear();
   _segments.clear();
 }

 /// return true if at least one [ps].collide != 0 (the Particles [ps] is included in the space)
 bool addParticles(Particles ps) {
   var b = false;
   for(int i = 0; i < ps.length; ++i) {
     var v = ps.collide[i];
     ps.collide[i] = v * v;
     b  = b || (ps.collide[i] != 0);
   }
   b = b && (ps.length > 0);
   if (b) {
     _particlesS.add(ps);
   }
   //if (ps.length > 0) print(">>>>>>>>>>>>>>>> ${ps.length} ${ps.collide[0]} ${b}");
   return b;
 }

 /// return true if [seg].collide != 0 (the Segment [seg] is include in the space)
 bool addSegment(Segment seg) {
   //print("try add segment");
   if (seg.collide != 0) {
     seg.collide = 1;
     _segments.add(seg);
     return true;
   }
   return false;
 }

 //TODO optimize with a grid, a quadtree, ...
 void handleCollision() {
   for (int i = 0; i < _particlesS.length; ++i) {
     _detectCollisionInterParticles(i);
     _detectCollisionParticlesSegments(i);
     _detectCollisionIntraParticles(i);
   }
 }

 void _detectCollisionInterParticles(int i) {
   var psA = _particlesS[i];
   for (int j = i+1; j < _particlesS.length; ++j) {
     var psB = _particlesS[j];
     for(int iA = 0; iA < psA.length; ++iA) {
       if (psA.collide[iA] != 0) {
         for(int iB = 0; iB < psB.length; ++iB) {
           if (psB.collide[iB] != 0) {
             if(checker.collideParticleParticle(psA, iA, psB, iB, _scol)){
               resolver.notifyCollisionParticleParticle(psA, iA, psB, iB, _scol.w);
             }
           }
         }
       }
     }
   }
 }

 void _detectCollisionIntraParticles(int i) {
   var psA = _particlesS[i];
   if (!psA.intraCollide) return;
   for(int iA = 0; iA < psA.length; ++iA) {
     if (psA.collide[iA] != 0) {
       for(int iB = iA+1; iB < psA.length; ++iB) {
         if (psA.collide[iB] != 0) {
           if(checker.collideParticleParticle(psA, iA, psA, iB, _scol)){
             resolver.notifyCollisionParticleParticle(psA, iA, psA, iB, _scol.w);
           }
         }
       }
     }
   }
 }

 void _detectCollisionParticlesSegments(int i) {
   var psA = _particlesS[i];
   for(int iS = 0; iS < _segments.length; ++iS) {
     var s = _segments[iS];
     if (psA == s.ps) continue;
     for(int iA = 0; iA < psA.length; ++iA) {
       if (psA.collide[iA] != 0) {
         //print("test ${psA.position3d[iA]}");
         if (checker.collideParticleSegment(psA, iA, s, _scol)) {
           resolver.notifyCollisionParticleSegment(psA, iA, s, _scol.w);
         }
       }
     }
   }
 }
}