重要な C# トピック

Nullable Reference Types

Nullable annotations help prevent NullReferenceException by distinguishing optional references from required ones.

How it works

Make possible null values visible to the compiler.

string? permits null. The null-coalescing operator supplies a safe fallback before Length is accessed.

Runnable C# example

Program.cs

using System;

class Program
{
    static void Main()
    {
        string? nickname = null;
        string displayName = nickname ?? "Anonymous";
        Console.WriteLine($"{displayName} ({displayName.Length})");
    }
}

Expected output

Anonymous (9)

Practice with the debugger

Set a breakpoint on an important assignment or condition, click Debug, and inspect the local values before stepping to the next line.