如何使用 null 条件运算符安全而简单地检查可为 null 的引用类型的属性

Question

Given code like:

Thing? maybeAThing = GetThing();

I want to write logic that safely checks if the object is not null and has a certain property:

if(maybeAThing is not null && maybeAThing.IsAGoodThing){... }

But this syntax seems a bit messy. I thought the null-conditional operators were supposed to let me do this as any test will fail as soon as null is encountered:

if(maybeAThing?.IsAGoodThing){...}

But this gives compiler error:

CS0266 cannot implicitly convert bool? to bool

It seems the 'nullableness' is extending to the return value ( bool? ) instead of the test failing as soon as maybeAThing is determined to be null .

Is this specific to NRTs rather than nullable value types? Is there a way to do this without having to write additional clauses, and if not then what is my misunderstanding in the way the language works?

Answer 1

You can write some variant of:

maybeAThing?.IsAGoodThing == true
maybeAThing?.IsAGoodThing ?? false
(maybeAThing?.IsAGoodThing).GetValueOfDefault(false)

You can also use a property pattern:

maybeAThing is { IsAGoodThing: true }

Answer 2

You can just write:

if(maybeAThing?.IsAGoodThing == true){...}


null == true  //Nope
false == true //Nope
true == true  //Yes

Answer 3

You can use

if(maybeAThing?.IsAGoodThing == true){...}

This converts the Nullable<bool> to a bool .

Lifted Operators

For the equality operator ==, if both operands are null, the result is true, if only one of the operands is null, the result is false; otherwise, the contained values of operands are compared.