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Maybe<T>

One of the most insidious bug producers in .NET code is the null value. Do you return null to mean "no value"? What's the caller supposed to do with that? Did you mean there was an error? Did you mean there wasn't an error but you can't give an answer? Did you mean the answer was empty? Or did someone just forget to initialize the variable?

I wrote this class long before Microsoft came up with their oddly-named nullable reference types feature, and I'm not a fan of Microsoft's solution to the Null Reference problem. I think their Nullable Reference Types [sic] are clumsy and make the code look ugly and noisy. They couldn't even get the name right - reference types were always nullable! Perhaps I'm biased because this is the way I chose to solve that problem, but I still prefer to use Maybe<T> to clearly communicate my intent to my users.

The ambiguity around "error" vs. "no value" is why we created Maybe<T>.

Maybe<T> is a type that either has a value, or doesn't, but it is never null. The idea is that by using a Maybe<T> you clearly communicate your intentions to the caller. By returning Maybe<T> you nail down the ambiguity: "there might not be a value and you have to check".

Strictly, a Maybe<T> is an IEnumerable<T> which is either empty (no value) or has exactly one element. Because it is IEnumerable you can use certain LINQ operators:

  • maybe.Any() will be true if there is a value.
  • maybe.Single() gets you the value.
  • maybe.SingleOrDefault() gets you the value or null, if you really wanted a null.

Creating a maybe can be done by:

  • object.AsMaybe(); - wrap a non-null object.
  • Maybe<int>.From(7); - works with value types, and also safe for null references.
  • Maybe<T>.Empty - a maybe without a value.

Maybe<T> has a ToString() method so you can write it to a stream or use in a string interpolation, and you will get the serialized value or "{no value}".

Try returning a Maybe<T> whenever you have a situation wehere there may be no value, instead of null. You may find that your bug count tends to diminish.