Woking with Packed Arrays, accessing data

Question

I'm working with a large image array, so i've packed it. To access the pixels in the array i've implemented two methods.

def get_p(a)
  data=a.unpack('S9s')
end
def put_p(array,index_a,value)
  index=index_a[0]
  k=array.unpack('S9s')
  k[index]=value
  k.pack('S9s')
end

It works, but i wondered if there was a more elegant way to do this. Makes my code look different than my standard array functions.

If get_p(image_data[i][j+1])[BLOB]==0

vs

if image_data[i][j+1][BLOB]==0

Also, don't know if anyone cares, but unpack doesn't seem to be documented anywhere, i was lucky to find a reference here, but it took some time.

Answer 1

You could craete a class like:

class PackedArray

  def initialize(array)
    @packed_array = array.pack('S9s')
  end

  def [](key)
    data = @packed_array.unpack('S9s')
    data[key]
  end

  def []=(key, val)
    k = @packed_array.unpack('S9s')
    k[key]=val
    @packed_array = k.pack('S9s')
  end
end

Then, fill your image_data[i][j] with an instance of this class. E.g.

for i in [0..image_data.size]
  for j in [0..image_data[i].size]
    image_data[i][j] = new PackedArray(image_data[i][j])  
  end
end

And finally you can simply use:

if image_data[i][j+1][BLOB] == 0

Without needing of packing/unpacking manually.