Checking a bool value with a generic in C#

Question

I have the following method:

void Test<T>(T Result)

and I need to implement something like this:

if Result is null, or T is a bool and that bool is false

I tried to do something like

if (typeof(T) == typeof(bool)
{
  if ((bool)Result == false)   // doesn't work
  if (Result as bool == false) // doesn't work

how can I implement this without creating two methods?

what you are asking for is called template specialization. The closest equivalent to this in C# is overloading, see the answer I proposed as duplicate. — Cee McSharpface, Sep 03 '17 at 17:24
Adding a constraint to you method `Test(T Result) where T : IComparable` makes it *comparable*. `Result.CompareTo(true)==0` — L.B, Sep 03 '17 at 17:28
`if (someBool == false)` is never useful anyway. Just use `if(!someBool)` — oerkelens, Sep 03 '17 at 17:28
@oerkelens I think you mean `if(!someBool)` which is not more readable. — L.B, Sep 03 '17 at 17:30

score 2 · Accepted Answer · answered Sep 03 '17 at 17:32

2

You can try casting it to a nullable bool and test it:

public void Test<T>(T result)
{
    var asBool = result as bool?;
    if (!asBool.HasValue || !asBool.Value)
    {
        // do whatever
    }
}

(I changed Result to result since it is a parameter)

answered Sep 03 '17 at 17:32

oerkelens

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this works! thanks! – Thomas Sep 03 '17 at 17:34

trashr0x · Answer 2 · 2017-09-03T17:58:26.627

0

Here's another solution which casts T to bool via object (you can't cast T to bool directly):

if ((bool)(object)result == false)
{
    // bool with value set to false
}

You might also want to consider benchmarking all solutions proposed in the answers if performance is a concern—see "Performance surprise with “as” and nullable types".

edited Sep 03 '17 at 17:58

answered Sep 03 '17 at 17:49

trashr0x

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Performance is not an issue here but thanks for the link, it's interesting! – Thomas Sep 03 '17 at 18:21

score 0 · Answer 3 · answered Sep 03 '17 at 20:07

0

You can test with

if (EqualityComparer<T>.Default.Equals(result, default(T))) {
    ...
}

For bool, default(T) is false, for reference types it is null. For all other types, it is a value represented by all bits set to 0. I.e. for numeric types it will be 0.

answered Sep 03 '17 at 20:07

Olivier Jacot-Descombes

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Checking a bool value with a generic in C#

3 Answers3