Cannot implicitly convert type bool?

Question

I am trying to convert my nullable bool value and I am getting this error.

Cannot implicitly convert type 'bool?' to 'bool'. An explicit conversion exists (are you missing a cast?)

For example:

public virtual bool? MyBool
  {
    get;
    set;
  }

if (!MyBool){}

I don't think this is too confusing, it is just Ternary Logic: http://en.wikipedia.org/wiki/Three-valued_logic - I actually like it because I like the notion of something having no value. In other words, uninitialized vs. initialized. — dyslexicanaboko, Jul 02 '12 at 04:06

score 30 · Accepted Answer · answered Feb 01 '12 at 01:33

30

As the error states, you can't use a bool? in a conditional. (What would happen if it's null?)

Instead, you can write if (MyBool != true) or if (MyBool == false), depending on whether you want to include null. (and you should add a comment explaining that)

answered Feb 01 '12 at 01:33

SLaks

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Another valid check is `MyBool ?? false`, although I generally prefer `MyBool.GetValueOrDefault()`. – Anthony Pegram Feb 01 '12 at 01:41
@AnthonyPegram: However, that requires extra parentheses for negation, and is also more confusing. – SLaks Feb 01 '12 at 01:51
I do not disagree on the first, but I don't find the second any more difficult to use or understand. Generally, I do not like direct comparisons to true or false, although I do exactly that in Linq-to-EF queries because the method is not supported. – Anthony Pegram Feb 01 '12 at 01:58

score 9 · Answer 2 · answered Feb 01 '12 at 01:33

You have to use MyBool.Value

for example:

if (!MyBool.Value) { }

However, you should test that it does indeed have a value to begin with. This tests that MyBool has a value and it is false.

if (MyBool.HasValue && !MyBool.Value) { }

Or you might really want the following that runs the code block if it either has not been assigned or has is false.

if (!MyBool.HasValue || !MyBool.Value) { }

The question really boils down to whether you truly intended to have a nullable boolean variable and, if so, how you want to handle the 3 possible conditions of null, true or false.

score 2 · Answer 3 · answered Feb 01 '12 at 01:44

2

You need to check if it has a value. What do you want to do if MyBool == null?

if( MyBool.HasValue && !MyBool.Value ) // MyBool is false
if( MyBool.HasValue && MyBool.Value ) // MyBool is true
if( !MyBool.HasValue ) // MyBool is null

answered Feb 01 '12 at 01:44

The Real Baumann

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Cannot implicitly convert type bool?

3 Answers3

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