C# \ Dynamic \ can I check in one statement if dynamic var is null (object type) or zero (value type)

Question

Is there a support in C# 4.0 to do that in one line?

I did for objects:

 if (ReferenceEquals(null, myDynamicVar))

so now I need to see if this a zero. how to do it and is there a statement that can do both?

Why do you think a `ValueType` is always zero? `bool` for example is `false` (this is not zero). See here: http://stackoverflow.com/questions/325426/programmatic-equivalent-of-defaulttype — Amiram Korach, Aug 15 '12 at 14:13

score 4 · Accepted Answer · answered Aug 15 '12 at 14:13

4

if (ReferenceEquals(null, myDynamicVar) || Equals(0, myDynamicVar)) ...

answered Aug 15 '12 at 14:13

Tim Rogers

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Thank you all - I'll use this. – user1025852 Aug 15 '12 at 14:26
1

You're welcome to use what you want, and this does answer your question exactly, but please bear in mind Amiram's comment when implementing. – Jaime Torres Aug 15 '12 at 14:33
watch out if myDynamicVar would have value of DateTime.MinValue – Ilya Ivanov Aug 15 '12 at 15:05

score 3 · Answer 2 · answered Aug 15 '12 at 14:15

3

public bool IsDefault<T>(T value)
{
    if(value == null) return true;
    return value.Equals(default(T));
}

int v = 5;
object o = null;
IsDefault(v); //False
IsDefault(0); //True
IsDefault(o); //True
IsDefault("ty"); //False

answered Aug 15 '12 at 14:15

Ilya Ivanov

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Unfortunately, if `o` was type dynamic, like in the question, this code would not work. – jbtule Aug 15 '12 at 14:51
you can try to call it IsDefault(o) and it will work. The case is that it will return false if dynamic o = 0; That's why you shouldn't use dynamic is it is unnecessary. – Ilya Ivanov Aug 15 '12 at 15:02
the case of Tim Rogers won't work if dynamic o = DateTime.MinValue – Ilya Ivanov Aug 15 '12 at 15:04
Actually all you need to make yours work for every case is an overload `public bool IsDefault(object value) { return (value == null); }` The dynamic binder would choose the generic form except when it's null and then it would choose the object version. – jbtule Aug 15 '12 at 16:21

Jaime Torres · Answer 3 · 2012-08-15T14:31:47.663

2

Sloppy:

if (ReferenceEquals(null, myDynamicVar) || myDynamicVar ==
   (myDynamicVar.GetType().IsValueType ? Activator.CreateInstance(myDynamicVar.GetType()) : null)
{
    //Code greatness
}

Cleaner:

    public static bool IsDefault(dynamic input)
    {
        if (input == null)
        {
            return true;
        }
        else if (input.GetType().IsValueType)
        {
            return input == Activator.CreateInstance(input.GetType());
        }
        else
        {
            return false;
        }
    }

edited Aug 15 '12 at 14:31

answered Aug 15 '12 at 14:15

Jaime Torres

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Doesn't compile. `default` requires the type name, not `Type` instance. – Amiram Korach Aug 15 '12 at 14:17
That was a stupid mistake... fixed. Thanks for pointing that out. – Jaime Torres Aug 15 '12 at 14:32

C# \ Dynamic \ can I check in one statement if dynamic var is null (object type) or zero (value type)

3 Answers3