New() in constructor

Question

Can someone tell me what New() in the following method constructor means? I know that TEvent inherits from CompositePresentationEvent but what does new() mean?

protected void RaiseEvent<TEvent, TParameter>(TParameter parameter) where TEvent : 
    CompositePresentationEvent<TParameter>, new()
    {
        EventAggregator.GetEvent<TEvent>().Publish(parameter);
    }

Note that this method is not a constructor: **1.** You would not specify a return type with a constructor. **2.** You would not specify generic type parameters with a constructor; you would specify them at the type level. — stakx - no longer contributing, Mar 29 '13 at 23:01

Mike Dinescu · Answer 1 · 2013-03-29T22:54:58.333

4

In that function declaration new() is a constraint on the TEvent generic type parameter. It means the type must be have a public constructor without parameters.

Read more about constraints on generic types here.

edited Mar 29 '13 at 22:54

answered Mar 29 '13 at 22:53

Mike Dinescu

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Close - it means that the type can be created and must have a parameterless constructor. You are thinking of the `class` constraint. – Matt Johnson-Pint Mar 29 '13 at 22:55
From the link you provided: "The type argument must have a public parameterless constructor. When used together with other constraints, the new() constraint must be specified last." – Phil Mar 29 '13 at 22:57

MeTitus · Accepted Answer · 2013-03-30T01:40:29.067

1

That is a constraint on the generic parameter of your method. It basically means that the generic type being passed as an argument to your method must have a parameterless constructor.

edited Mar 30 '13 at 01:40

answered Mar 29 '13 at 22:57

MeTitus

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New() in constructor

2 Answers2