C# 7.0 Discards - Discard Variable

Giriş
Açıklaması şöyle

Discards are local variables which you can assign but cannot read from. i.e. they are “write-only” local variables.

Discard Variable 2 durumda kullanılabilir.

1. Out Variable

2. Return Value

Örnek - Out Variable
Şöyle yaparız.

if (bool.TryParse("TRUE", out bool _))

Örnek - İkisi Birlikte

Şöyle yaparız

// Out params

if (DateTime.TryParse(dateString, out _))
    Console.WriteLine("dateString can be parsed as a DateTime");

// Tuples

var (minimum, _) = FindMinMax(myData);
Console.WriteLine($"The minimum value is {minimum}");

Örnek - Return Value
Tuple dönen bir metod için şöyle yaparız.

public static void Main()
{
    var (_, _, _, pop1, _, pop2) = QueryCityDataForYears("New York City", 1960, 2010);
    Console.WriteLine($"Population change, 1960 to 2010: {pop2 - pop1:N0}");
}

private static (string, double, int, int, int, int)
  QueryCityDataForYears(string name, int year1, int year2)
{
  int population1 = 0, population2 = 0;
  double area = 0;

  if (name == "New York City")
  {
     area = 468.48;

     if (year1 == 1960) {
       population1 = 7781984;
    }

    if (year2 == 2010) {
      population2 = 8175133;
    }

    return (name, area, year1, population1, year2, population2);
  }

  return ("", 0, 0, 0, 0, 0);
}