Best way to check for nullable bool in a condition expression (if ...)

I was wondering what was the most clean and understandable syntax for doing condition checks on nullable bools.

Is the following good or bad coding style? Is there a way to express the condition better/more cleanly?

bool? nullableBool = true;
if (nullableBool ?? false) { ... }
else { ... }

especially the if (nullableBool ?? false) part. I don't like the if (x.HasValue && x.Value) style ...

(not sure whether the question has been asked before ... couldn't find something similar with the search)

I think a lot of people concentrate on the fact that this value is nullable, and don't think about what they actually want :)

bool? nullableBool = true;
if (nullableBool == true) { ... } // true
else { ... } // false or null

Or if you want more options...

bool? nullableBool = true;
if (nullableBool == true) { ... } // true
else if (nullableBool == false) { ... } // false
else { ... } // null

(nullableBool == true) will never return true if the bool? is null :P

How about using GetValueOrDefault, which is pretty self-explaining and allows to use whatever default you want:

if (nullableBool.GetValueOrDefault(false)) {
}

You may not like it, but personally I find

if (x.HasValue && x.Value)

the most readable. It makes it clear you are working with a nullable type and it makes it clear you are first checking whether the nullable type has a value before acting on it conditionally.

If you take your version and replace the variable with x also it reads:

if (x ?? false)

Is that as clear? Is it obvious x is a nullable type? I'll let you decide.

If you want to treat a null as false, then I would say that the most succinct way to do that is to use the null coalesce operator (??), as you describe:

if (nullableBool ?? false) { ... }

Another way is to use constant pattern matching:

if (nullableBool is true) {}
if (nullableBool is false) {}
if (nullableBool is null) {}

Unlike the operator ==, when reading the code, this will distinguish the nullable type check from ordinary "code with a smell".

Just think of bool? as having 3 values, then things get easier:

if (someNullableBool == true)     // only if true
if (someNullableBool == false)    // only if false
if (someNullableBool == null)     // only if null

Actually I think that (nullableBool ?? false) is a legitimate option especially when you are trying to evaluate a nullable bool in linq.

For example:

array.Select(v => v.nullableBool ?? false)
(from v in array where v.nullableBool ?? false)

Is cleaner in my opinion as opposed to:

array.Select(v => v.nullableBool.HasValue ? v.nullableBool.Value : false)
(from v in array where v.nullableBool.HasValue ? v.nullableBool.Value : false)

Use extensions.

public static class NullableMixin {
    public static bool IsTrue(this System.Nullable<bool> val) {
        return val == true;
    }
    public static bool IsFalse(this System.Nullable<bool> val) {
        return val == false;
    }
    public static bool IsNull(this System.Nullable<bool> val) {
        return val == null;
    }
    public static bool IsNotNull(this System.Nullable<bool> val) {
        return val.HasValue;
    }
}


Nullable<bool> value = null;
if(value.IsTrue()) {
// do something with it
}
     

Lets check how the comparison with null is defined:

static void Main()
    {
        Console.WriteLine($"null != null  => {null != null}");
        Console.WriteLine($"null == null  => {null == null}");
        Console.WriteLine($"null != true  => {null != true}");
        Console.WriteLine($"null == true  => {null == true}");
        Console.WriteLine($"null != false => {null != false}");
        Console.WriteLine($"null == false => {null == false}");
    }

and the results are:

null != null  => False                                                                                                                                                                                                                                  
null == null  => True                                                                                                                                                                                                                                   
null != true  => True                                                                                                                                                                                                                                   
null == true  => False                                                                                                                                                                                                                                  
null != false => True                                                                                                                                                                                                                                   
null == false => False

So you can safely use:

// check if null or false
if (nullable != true) ...

// check if null or true
if (nullable != false) ...

// check if true or false
if (nullable != null) ...

If you only want to test for true against null/false, One I've just used and reads quite well is

bool? someCondition = null
if (someCondition.Equals(true))
...

I think its up to you. I certainly think the .HasValue approach is more readable, especially with developers not familiar with the ?? syntax.

The other point of a nullable boolean type is that it is tristate, so you may want to do something else when it is just null, and not default to false.

Given enum

public enum PublishMode { Edit, View }

you can do it like here

 void MyMethod(PublishMode? mode)
    {
       var publishMode = mode ?? PublishMode.Edit;
       
//or
       if (mode?? PublishMode.Edit == someValue)
       ....
    }

If you're in a situation where you don't have control over whether part of the condition is checking a nullable value, you can always try the following:

if( someInt == 6 && someNullableBool == null ? false : (bool)someNullableBool){
    //perform your actions if true
}

I know it's not exactly a purist approach putting a ternary in an if statement but it does resolve the issue cleanly.

This is, of course, a manual way of saying GetValueOrDefault(false)