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Smalltalk Matrix nil error

So im running this code in playground of pharos 6.0 and it gives me an error saying "unindex object is not access able. Basically, I'm trying to make a matrix that is 8x10. How do I make one?

  | aMatrix row col|


  aMatrix := Matrix new.
  aMatrix numberOfColumns: 3.
  aMatrix numberOfRows: 3. 
  aMatrix at: 2 at: 2 put: 6.
Solution

  • If you try to make a matrix 8x10 why do you do

    aMatrix numberOfColumns: 3.
aMatrix numberOfRows: 3.

    ?

    I checked the code, and I don't get why it is implemented the way it is implemented. numberOfColumns: and numberOfRows: just assign the parameter to an instance variable, but don't change the internal data structure.

    You should do something like:

    aMatrix := Matrix rows: 8 columns: 10.   
aMatrix at: 2 at: 2 put: 6.