CODEWITHSUNDEEP
c#.netgenericstypesinterface
Matias Cicero
Matias Cicero

Reputation: 26281

Generic Constraint for Non Nullable types

I have the following class:

public class KeyDTO<T>
{
     public T Id { get; set; }
}

So far so good, but I want the type parameter T to be a non-nullable type. I've read somewhere that this may be feasible:

public class KeyDTO<T> where T : IComparable, IComparable<T>
{
     public T Id { get; set; }
}

But, If i change public T Id to public T? Id, I get a compilation error telling me that T must be non-nullable.

How can I specify that a generic type parameter must be non-nullable?

Edit

I want to accomplish this because I want to annotate my Id property with the [Required] attribute as follows:

public class KeyDTO<T> {
    [Required]
    public T Id { get; set; }
}

What [Required] does is validate the model so T cannot be null.

However, if I have KeyDTO<int>, Id will be initialized to 0, bypassing my [Required] attribute

Upvotes: 63

Views: 41262

Answers (2)

nalka
nalka

Reputation: 2360

From C# 8.0 you can now use the where T : notnull generic constraint to specificy T is a non-nullable type.

Upvotes: 118

Servy
Servy

Reputation: 203821

Applying where T : struct applies a generic constraint that T be a non-nullable value type. Since there are no non-nullable reference types, this has the exact same semantics as simply "all non-nullable types". Nullable value types (i.e. Nullable<T>) do not satisfy the struct generic constraint.

Upvotes: 45

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