Just started programming in the Nim language (which I really like so far). As a learning exercise I am writing a small matrix library. I have a bunch more code, but I'll just show the part that's relevant to this question.
type Matrix*[T; nrows, ncols: static[int]] = array[0 .. (nrows * ncols - 1), T] # Get the index in the flattened array corresponding # to row r and column c in the matrix proc index(mat: Matrix, r, c: int): int = result = r * mat.ncols + c # Return the element at r, c proc ``(mat: Matrix, r, c: int): Matrix.T = result = mat[mat.index(r, c)] # Set the element at r, c proc `=`(mat: var Matrix, r, c: int, val: Matrix.T) = mat[mat.index(r, c)] = val # Add a value to every element in the matrix proc `+=`(mat: var Matrix, val: Matrix.T) = for i in 0 .. mat.high: mat[i] += val # Add a value to element at r, c proc `+=`(mat: var Matrix, r, c: int, val: Matrix.T) = mat[mat.index(r, c)] += val # A test case var mat: Matrix[float, 3, 4] # matrix with 3 rows and 4 columns mat[1, 3] = 7.0 mat += 1.0 # add 8.0 to entry 1, 3 in matrix `+=`(mat, 1, 3, 8.0) # works fine
All this works fine, but I'd like to be able to replace the last line with something like
mat[1, 3] += 4.0
This won't work (wasn't expecting it to either). If I try it, I get
Error: for a 'var' type a variable needs to be passed
How would I create an addition assignment operator that has this behavior? I'm guessing I need something other than a proc to accomplish this.