Nullable and Pattern Matching

Null Coalescing

The null-coalescing operator chooses a fallback for a null value.

null coalescing The `??` operator returns the left value unless it is null.

Null Coalescing

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

class Program
{
    static void Main()
    {
        int? count = null;
        int fallback = 1;
        int display = count ?? fallback;

        Console.WriteLine($"hasCount={count.HasValue}");
        Console.WriteLine($"display={display}");
    }
}

using System;

class Program
{
    static void Main()
    {
        int? count = 3;
        int fallback = 1;
        int display = count ?? fallback;

        Console.WriteLine($"hasCount={count.HasValue}");
        Console.WriteLine($"display={display}");
    }
}

  1. count ← (empty), fallback ← 1, display ← 1

    4{5    static void Main()6    {7        int? count→ (empty) = null; //@count=3, null8        int fallback→ 1 = 1;9        int display→ 1 = count(empty) ?? fallback1;1011        Console.WriteLine($"hasCount={count.HasValueFalse}");12        Console.WriteLine($"display={display1}");13    }
    outputhasCount=False
display=1

  1. count ← 3, fallback ← 1, display ← 3

    4{5    static void Main()6    {7        int? count→ 3 = 3;8        int fallback→ 1 = 1;9        int display→ 3 = count3 ?? fallback1;1011        Console.WriteLine($"hasCount={count.HasValueTrue}");12        Console.WriteLine($"display={display3}");13    }
    outputhasCount=True
display=3