CODEWITHSUNDEEP
c#generics
user1479794
user1479794

Reputation: 71

new() in method

Having these classes:

public interface IDbContextFactory
{
    DbContext GetContext();
}

public class Repo<T> : IRepo<T> where T : Entity, new()
{
    protected readonly DbContext c;
}

public Repo(IDbContextFactory f)
{
    c = f.GetContext();
}

What does the keyword new() (in class Repo<T>) do?

Upvotes: 4

Views: 146

Answers (3)

Jodrell
Jodrell

Reputation: 35716

When you use the where keyword on a generic definition you apply a type contraint to the generic paramater. The new() constraint declares that the type, T in this case, must have a default constructor. http://msdn.microsoft.com/en-us/library/sd2w2ew5.aspx

After reading your clarification disguised as an answer I thought I would try and help by clarifying a couple of things.

The code in your orginal question defines an interface that seemes to be used by a disembodied constructor. In between those two denfinitions you have defined a generic class which doesen't seem to do much.

Your question pertains to the generic class and the other two definitions are irrelavent to both the question and the answer.

Upvotes: 1

David M
David M

Reputation: 72860

It means that the type T must expose a public, default (i.e. parameterless) constructor. That is, you will be able to construct an instance of T with new T(). It can expose other constructors as well, but this generic constraint makes the default one mandatory.

Upvotes: 11

DarthVader
DarthVader

Reputation: 55022

it means, the entity should have a parameterless public constructor.

see this.

Upvotes: 3

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