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public readonly double Distance => Math.Sqrt(X * X + Y * Y);

public static bool IsLetterOrSeparator(this char c) =>
    c is (>= 'a' and <= 'z') or (>= 'A' and <= 'Z') or '.' or ',';

static Quadrant GetQuadrant(Point point) => point switch
{
    (0, 0) => Quadrant.Origin,
    var (x, y) when x > 0 && y > 0 => Quadrant.One,
    var (x, y) when x < 0 && y > 0 => Quadrant.Two,
    var (x, y) when x < 0 && y < 0 => Quadrant.Three,
    var (x, y) when x > 0 && y < 0 => Quadrant.Four,
    var (_, _) => Quadrant.OnBorder,
    _ => Quadrant.Unknown
};

Chris Maunder wrote:

C#

public readonly double Distance => Math.Sqrt(X * X + Y * Y);

That would give you a CS0106 compiler error.
You would need either:

C#

public readonly double Distance = Math.Sqrt(X * X + Y * Y);

or:

C#

public double Distance => Math.Sqrt(X * X + Y * Y);

Chris Maunder wrote:

C#

c is (>= 'a' and <= 'z') or (>= 'A' and <= 'Z')

(uint)((c | 0x20) - 'a') <= 'z' - 'a'

Richard Deeming wrote:

That would give you a CS0106 compiler error

Richard Deeming wrote:

That would give you a CS0106 compiler error.

Kornfeld Eliyahu Peter wrote:

Be more positive - learn these additions, but use only if fits...
After all - they do not force you!!!

private void DroppedURL_DoWork(object sender, DoWorkEventArgs e)
     {
     if (sender is BackgroundWorker worker)
         {
         ...

private void DroppedURL_DoWork(object sender, DoWorkEventArgs e)
     {
     BackgroundWorker worker = sender as BackgroundWorker;
     if (worker != null)
         {
         ...