Question

I have a MapTile class which holds a tile sprite and the tile’s attribute. I want to create a 2D array which holds for example 100 tiles in a 10×10 grid. I have drawn a tile map using a plain old 2D array holding only the tile sprite and that worked fine. However, now when I assign a tile sprite to the 2D Array named mapData containing MapTile classes and using mapData[i][j].tileSprite = tileNum, every element in the column is assigned the tileNum value. I have tried everything I could think of to get this to work. I am a C++ programmer new to Ruby.

class MapTile
attr_accessor :tileSprite, :attribute

    def initialize(sprite, attr)
    @tileSprite = sprite
    @attribute = attr
    end 

    def tileSprite
        @tileSprite
    end

    def attribute
        @attribute
    end

end



def array2D(width,height)
  a = Array.new(width, MapTile.new(123,0))
  a.map! { Array.new(height, MapTile.new(123,0)) }
  return a
end


@mapData = array2D(@mapSize,@mapSize)

mapData[1][j].tileSprite = tileNum  #Now every tileSprite in column 1 is tileNum

Solution

Changed the array2D method to

def array2D(width,height)
a = Array.new(width) { MapTile.new(10,0)}
a.map! { Array.new(height) { MapTile.new(10,0) } }
return a
end

Thanks Michael!

Answer 1

You are using the same object for each array element. Try Array.new(width) { MapTile.new(123,0) } instead.

From the docs:

# only one copy of the object is created 
a = Array.new(2, Hash.new)

# here multiple copies are created 
a = Array.new(2) { Hash.new }

BTW: There are some things in your code that are rather unidiomatic Ruby, you may want to run that by the Code Review Stack Exchange.