Why Do Some C# and .NET Corner Cases Defy Expectations?

Exploring Unexpected Behaviors in C# and .NET

Building robust applications requires a deep understanding of edge cases. C# and .NET, while powerful, present some surprising scenarios that challenge common assumptions. Let's examine a few examples illustrating these unusual behaviors:

When new Doesn't Produce a New Object

Consider this seemingly straightforward code:

<code class="language-csharp">string x = new string(new char[0]);
string y = new string(new char[0]);
Console.WriteLine(object.ReferenceEquals(x, y)); // Prints True</code>

One might expect new to always create distinct objects for reference types. However, C#'s special handling of empty strings leads to x and y referencing the same object.

Nullable Types and the NullReferenceException

This code snippet highlights a puzzling interaction with nullable types:

<code class="language-csharp">static void Foo<T>() where T : new()
{
    T t = new T();
    Console.WriteLine(t.GetType()); // Throws NullReferenceException
}</code>

Even though t is initialized, calling GetType() throws a NullReferenceException. This is because if T is a nullable type (like int?), the implicit boxing to object can result in a null value, causing the exception when GetType() is called on the boxed null.

The Case of the Null new Instance

This scenario demonstrates a less intuitive possibility:

<code class="language-csharp">public static void CanThisHappen<T>() where T : class, new()
{
    var instance = new T(); // new() on a ref-type; should be non-null
    Debug.Assert(instance != null, "How did we break the CLR?");
}</code>

The constraints suggest T is a reference type instantiable with new. However, techniques like remoting (e.g., using a proxy that returns null) can bypass this expectation, leading to the assertion failing. This highlights the complexities introduced when dealing with advanced features like remoting.

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