Today is the last day of the 2018 Blogging A-to-Z challenge. Today's topic: Nothing. Zero. Nada. Zilch. Null.
The concept of "zero" only made it into Western mathematics just a few centuries ago, and still has yet to make it into many developers' brains. The problem arises in particular when dealing with arrays, and unexpected nulls.
In C#, arrays are zero-based. An array's first element appears at position 0:
var things = new[] { 1, 2, 3, 4, 5 };
Console.WriteLine(things[1]);
// -> 2
This causes no end of headaches for new developers who expect that, because the array above has a length of 5, its last element is #5. But doing this:
Console.WriteLine(things[5]);
...throws an IndexOutOfRange exception.
You get a similar problem when you try to read a string, because if you recall, strings are basically just arrays of characters:
var word = "12345";
Console.WriteLine(word.Substring(4));
// 5
Console.WriteLine(word.Substring(5));
// IndexOutOfRange exception
The funny thing is, both the array things and the string word have a length of 5.
The other bugaboo is null. Null means nothing. It is the absence of anything. It equals nothing, not even itself (though this, alas, is not always true).
Reference types can be null, and value types cannot. That's because value types always have to have a value, while reference types can simply be a reference to nothing. That said, the Nullable<T> structure gives value types a way into the nulliverse that even comes with its own cool syntax:
int? q = null;
int r = 0;
Console.WriteLine(q ?? 0 + r);
// 0
(What I love about this "struct?" syntax is you can almost hear it in a Scooby Doo voice, can't you?)
Line 1 defines a nullable System.Int32 as null. Line 2 defines a bog-standard Int32 equal to zero. If you try to add them, you get a NullReference exception. So line 3 shows the coalescing operator that basically contracts both of these statements into a succinct little fragment:
// Long form:
int result;
if (q.HasValue)
{
result = q.Value + r;
}
else
{
result = 0 + r;
}
// Shorter form:
int result = (q.HasValue ? q.Value : 0) + r;
// Shortest form:
int result = q ?? 0 + r;
And so the Daily Parker concludes the 2018 Blogging A-to-Z challenge with an entire post about nothing. I hope you've enjoyed the posts this month. Later this morning, I'll post the complete list of topics as a permanent page. Let me know what you think in the comments. It's been a fun challenge.