C# reference type conditional without comparator

Question

I see this sort of thing in javascript all the time, iffy/falsy statements

if (someUnknownType) {
    // will check null | undefined | 0 | false | ''
}

but I've encountered this today in C# for the first time and I can't find seem to find the right words that I can search for this.

_existingInstance = getTheInstanceOrNull();
if (_existingInstance)
    DoSomeThings();

I thought it was odd since it didn't explicitly say existingInstance != null, so I decided to test out a couple things

if (null)
    DoSomeThings();

// Err: Cannot convert null to 'bool' because it is non-nullable

I double checked the return type of the method in question, and ended up testing this next

MyType instance = null;
if (instance)
    DoSomeThings(); // Roslyn says it's okay

Which I suspected would pass, since it's the source of my doubt. I then proceeded to test one last scenario

bool? doNotPass = null;
if (doNotPass)
    DoSomeThings(); 

// Err: Cannot implicitly convert 'bool?' to 'bool'

What exactly is being checked when a reference type is not explicitly checked against a comparator in a conditional?

I'be been working with C# for a few years now, so if it's well known, is this simply unpopular?

As a last note, I looked at the class definition to make sure there was no operator overload, and I didn't see any

What does `getTheInstanceOrNull`? Is this by any chance run on Unity3d? — Camilo Terevinto, Sep 02 '18 at 16:10
yes, this is in unity. It returns an instance of a class that inherits from `MonoBehaviour` or null if a ray cast fails — Felipe, Sep 02 '18 at 16:13
Any class can implement operators that support *conversion* to `bool`. — Damien_The_Unbeliever, Sep 02 '18 at 16:16
@Damien_The_Unbeliever Or the true/false operators. Interesting discussion in the duplicate — Camilo Terevinto, Sep 02 '18 at 16:17

score 0 · Answer 1 · answered Sep 02 '18 at 16:12

0

first, bool? is not a reference type. it’s actually a struct, which is a value type. it’s a shortcut to Nullable<bool>.

so that will fail in your comparison.

this was throwing you off.

answered Sep 02 '18 at 16:12

Erik Funkenbusch

1 Answers1