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public void Foo<T>(Func<T> bar)
where T: IMyInterface
{
Func<IMyInterface> func = bar;
}
It has been a while since I'd understood covariance, but shouldn't this compile?
Anything bar can return is also an IMyInterface. What seems to be the problem?
488
Covariance and contravariance are terms that refer to the ability to use a more derived type (more specific) or a less derived type (less specific) than originally specified. Generic type parameters support covariance and contravariance to provide greater flexibility in assigning and using generic types.
In . NET Framework 4 and later versions, C# supports covariance and contravariance in generic interfaces and delegates and allows for implicit conversion of generic type parameters.
Covariance permits a method to have a return type that is a subtype of the one defined in the delegate. Contravariance permits a method to have a parameter type that is a base type of the one defined in the delegate type.
A type constraint on a generic type parameter indicates a requirement that a type must fulfill in order to be accepted as a type argument for that type parameter. (For example, it might have to be a given class type or a subtype of that class type, or it might have to implement a given interface.)
Is this a covariance bug in C# 4?
the correct code is:
public void Foo<T>(Func<T> bar)
where T: class, IMyInterface
{
Func<IMyInterface> func = bar;
}
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