text: /**
   * Records what objects are colliding with each other
   * @class ObjectCollisionMatrix
   */
  export class ObjectCollisionMatrix {
      /**
       * The matrix storage
       * @property matrix
       * @type {Object}
       */
      matrix = {};
  
      /**
       * @method get
       * @param  {Number} i
       * @param  {Number} j
       * @return {Number}
       */
      get(i, j) {
          i = i.id;
          j = j.id;
          if (j > i) {
              const temp = j;
              j = i;
              i = temp;
          }
          return i + '-' + j in this.matrix;
      }
  
      /**
       * @method set
       * @param  {Number} i
       * @param  {Number} j
       * @param {Number} value
       */
      set(i, j, value) {
          i = i.id;
          j = j.id;
          if (j > i) {
              const temp = j;
              j = i;
              i = temp;
          }
          if (value) {
              this.matrix[i + '-' + j] = true;
          } else {
              delete this.matrix[i + '-' + j];
          }
      }
  
      /**
       * Empty the matrix
       * @method reset
       */
      reset() {
          this.matrix = {};
      }
  
      /**
       * Set max number of objects
       * @method setNumObjects
       * @param {Number} n
       */
      setNumObjects(n) {
      }
  }