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new constraint (C# Reference)

  • Стаття

The new constraint specifies that a type argument in a generic class or method declaration must have a public parameterless constructor. To use the new constraint, the type cannot be abstract.

Apply the new constraint to a type parameter when a generic class creates new instances of the type, as shown in the following example:

class ItemFactory<T> where T : new()
{
    public T GetNewItem()
    {
        return new T();
    }
}

When you use the new() constraint with other constraints, it must be specified last:

public class ItemFactory2<T>
    where T : IComparable, new()
{  }

For more information, see Constraints on Type Parameters.

You can also use the new keyword to create an instance of a type or as a member declaration modifier.

C# language specification

For more information, see the Type parameter constraints section of the C# language specification.

See also