Maybe<int>.None.HasValue is true

[vkhorikov]

Maybe.None.HasValue is true

from csharpfunctionalextensions.

[vkhorikov]

Published 1.11.0

[FrancoisM]

It's because of

CSharpFunctionalExtensions/CSharpFunctionalExtensions/Maybe.cs

Line 22 in 744c14d

public bool HasValue => _value != null;

If it only works for T being a class then you should add where T: class

[FrancoisM]

Or better: replace with

public bool HasValue => _value != default;

[freakingawesome]

Or better: replace with

public bool HasValue => _value != default;

Comparing against default would have the side-effect of making zero a None value, which is probably unintentional.

I have submitted a pull request which wraps the value inside Maybe<T> in a class so that null checks work with structs as well as classes.

[FrancoisM]

Indeed in my case 0 is a None value but it may not always be the case.
I'm not sure about the wrapper.
The idea of Maybe is to give a type to null. As a struct cannot be null, then I think Maybe should not be used with a struct in the first place. My mistake. I'm more in favor of where T: class now that I think about it.

[freakingawesome]

I disagree that Maybe<T> is only about replacing null. It also gives you functor composability that otherwise wouldn't exist by using .Select(...). Here's a contrived example:

Maybe<string>.None.Select(_ => 42)

This would be impossible if we add the class type constraint, and currently this fails because the None maps to a Maybe<int> that has a value of zero, when logically it should map to None.

I updated my PR to fix these mapping issues as well.