Question

See the following code:

    List<Vector2> axes = new List<Vector2>();
    axes.Add(TopRight() - TopLeft());
    axes.Add(BottomLeft() - TopLeft());
    axes.Add(otherRectangle.TopRight() - otherRectangle.TopLeft());
    axes.Add(otherRectangle.BottomLeft() - otherRectangle.TopLeft());
    // Try normalizing vectors?
    foreach (Vector2 axis in axes)
    {
        axis.Normalize();
    }

the Vector2.Normalize() method is a void method that normalizes the vector it’s called on. Yet for some reason when I do this loop it doesn’t normalize the vectors. Am I just unable to modify a list this way?

Some oddities:

• Iterating with a for loop, i.e. axis[i].Normalize() doesn’t work.
• Iterating with the built-in List<T>.ForEach iterator does not work.
• Creating a normalizing the vector before adding it to the list rather than iterating over the list does work.

Why does iteration not work?

Answer 1

The foreach loop creates a local copy of the sequence element. You only normalize the copy.

You will need to do something like:

for(int i=0; i<axes.Count; i++)
    axes[i] = Vector2.Normalize(axes[i]);

This unintuitive behavior demonstrates, once again, why instance methods that mutate a struct are a bad idea.