Nullable and Pattern Matching

Nullable Value Types

A nullable value type can hold a normal value or null.

nullable value A nullable value type uses `?`, such as `int?`, to allow `null`.

Nullable Value Types

score
NullableValueTypes.cs
Replay: real traced execution (multi-file project)
using System;

class Program
{
    static void Main()
    {
        int? score = 90;
        bool hasScore = score.HasValue;
        int shown = score.GetValueOrDefault();

        Console.WriteLine($"hasScore={hasScore}");
        Console.WriteLine($"shown={shown}");
    }
}

using System;

class Program
{
    static void Main()
    {
        int? score = null;
        bool hasScore = score.HasValue;
        int shown = score.GetValueOrDefault();

        Console.WriteLine($"hasScore={hasScore}");
        Console.WriteLine($"shown={shown}");
    }
}

using System;

class Program
{
    static void Main()
    {
        int? score = 75;
        bool hasScore = score.HasValue;
        int shown = score.GetValueOrDefault();

        Console.WriteLine($"hasScore={hasScore}");
        Console.WriteLine($"shown={shown}");
    }
}

  1. score ← 90, hasScore ← True, shown ← 90

    4{5    static void Main()6    {7        int? score→ 90 = 90; //@score=null, 758        bool hasScore→ True = score.HasValueTrue;9        int shown→ 90 = score90.GetValueOrDefault();1011        Console.WriteLine($"hasScore={hasScoreTrue}");12        Console.WriteLine($"shown={shown90}");13    }
    outputhasScore=True
shown=90

  1. score ← (empty), hasScore ← False, shown ← 0

    4{5    static void Main()6    {7        int? score→ (empty) = null;8        bool hasScore→ False = score.HasValueFalse;9        int shown→ 0 = score(empty).GetValueOrDefault();1011        Console.WriteLine($"hasScore={hasScoreFalse}");12        Console.WriteLine($"shown={shown0}");13    }
    outputhasScore=False
shown=0

  1. score ← 75, hasScore ← True, shown ← 75

    4{5    static void Main()6    {7        int? score→ 75 = 75;8        bool hasScore→ True = score.HasValueTrue;9        int shown→ 75 = score75.GetValueOrDefault();1011        Console.WriteLine($"hasScore={hasScoreTrue}");12        Console.WriteLine($"shown={shown75}");13    }
    outputhasScore=True
shown=75