public string[] GetCountryList() => new string[] { "Russia", "USA", "UK" }; 

public string[] GetCountryList()
{
   return new string[] { "Russia", "USA", "UK" };
} 

public double Dist => Sqrt(X * X + Y * Y);

public double Dist(int X, int Y) => Math.Sqrt(X * X + Y * Y);

class Some 
{
  int X, Y;
  public double Dist => X*X + Y*Y;
}