IsNull revised

IsNull.cs

using System;

static class Program
{
	static void Main()
	{
		Test( "a" );
		Test( 1 );
		Test<int?>( 1 );
	}

	static void Test<T>( T nonNull)
	{
		Console.WriteLine( "IsNull<{0}>(default({0})) :{1}", typeof( T ).Name, NullChecker<T>.IsNull( default( T ) ) );
		Console.WriteLine( "IsNull<{0}>(nonNull) :{1}", typeof( T ).Name, NullChecker<T>.IsNull( nonNull ) );
	}
}

internal static class NullChecker<T>
{
	private static readonly Func<T, bool> _isNull =
		InitializeIsNull();

	private static Func<T, bool> InitializeIsNull()
	{
		if ( !typeof( T ).IsValueType )
		{
			return value => value == null;
		}

		var nullableUnderlyingType = Nullable.GetUnderlyingType( typeof( T ) );
		if ( nullableUnderlyingType != null )
		{
			return
				( Func<T, bool> )
				typeof( NullableNullChecker<> )
				.MakeGenericType( nullableUnderlyingType )
				.GetMethod( "IsNull" )
				.CreateDelegate( typeof( Func<T, bool> ) );
		}

		return _ => false;
	}

	public static bool IsNull( T value )
	{
		return _isNull( value );
	}
}

internal static class NullableNullChecker<T>
	where T : struct
{
	public static bool IsNull( Nullable<T> value )
	{
		return !value.HasValue;
	}
}