How to check if a generic type parameter is nullable?

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Determine if a generic param is a Nullable type

I'm trying to determine if a type parameter is Nullable.

    public T Get<T>(int index)
    {
        var none=default(T);
        var t = typeof(T);
        BaseVariable v = this[index].Var;
        if (T is Nullable) //compiler error
        {
            if (v == ... )
            {
                return none;
            }
        }
        //....
    }

How do I do this? I've tried doing t == typeof(Nullable) but that always resulted in false.

What I want to happen is for foo.Get<bool?>(1) to null at times.

This is a dup http://stackoverflow.com/questions/5181494/determine-if-a-generic-param-is-a-nullable-type — Nix, Jun 21 '11 at 16:32
@Nix that's in VB, so maybe borderline not a dupe. We'll see — Earlz, Jun 21 '11 at 16:34

score 58 · Answer 1 · answered Jun 21 '11 at 16:33

58

You can use Nullable.GetUnderlyingType:

var t = typeof(T);
// ...
if (Nullable.GetUnderlyingType(t) != null)
{
    // T is a Nullable<>
}

answered Jun 21 '11 at 16:33

LukeH

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This is not working in my version of .NET Core 3.1 with C#8.0 – niproblema Jan 28 '21 at 04:02
Works in net5.0/c#9, fwiw – JohnnyFun Nov 10 '21 at 00:59

How to check if a generic type parameter is nullable?

1 Answers1