17.3.3 canMove & collides

The method canMove is private. It will only be used inside this class, called from the collides method. The method should check if a particular square can move in a certain direction (the second argument).

Note that you should not move the square: only check if the movement is possible. For that reason it is not possible to use the Move method of class square. (It is also impossible to do so: precisely to avoid this error, the square is passed as a const reference.)

The method consists of the following steps:

• Create a local VecI2 with the square’s position.
• Move this position in the required direction. (Take another look at the move method in square if you have a trouble doing that.)
• Iterate over all elements in the container with squares and check whether that square is at the same position. If it is, the method should return false.
• If you reach the end of the container without finding a match, the method should return true. Indeed, if there is already a square would be on the new position, the function was abandoned during the audit. Meaning that the square can move in the requested direction.

The public method collides also has a direction argument, but with a const reference to a block. It is this method that will be used in the Tetris application.

Because a block has a method to retrieve a reference to the squares in the block, we use that first:

 
C Mems<square> & squares = b.getSquares();
 

The rest of the method will call the method canMove for each square. Even when only one square cannot move in the desired direction, the block collides with the pile. In this case the result will be false. Otherwise true is returned. Here’s the entire method:

 
bool collides(C block & b, DIRECTION dir) C 
{ 
  // Get squares from this block 
  C Mems<square> & squares = b.getSquares(); 
5 
  // check all of them 
  REPA(squares) 
{ 
     if(!canMove(squares[i], dir)) 
10 { 
        return true; 
 } 
} 
  return false; 
15}
 

Now that you have completed these methods, you can reuse your test application to verify this class.