# E0450: misleading use of ',' operator in index

Using comma operator within an indexing operation is misleading, as it can be confused with a new array definition, or with access to multiple elements of the container.

For example:

    let matrix = [
      [1, 2, 3],
      [4, 5, 6],
      [7, 8, 9],
    ];
    let topLeft = matrix[0, 0];

Here, the value of `topLeft` will be equal to `matrix[0] = [1, 2, 3]`. If the intention is to find the value at the top-left corner of `matrix`, the correct syntax would be:

    let matrix = [
      [1, 2, 3],
      [4, 5, 6],
      [7, 8, 9],
    ];
    let topLeft = matrix[0][0]; // topLeft = 1

Documentation for other errors