使用一个实现的接口来实例化具有多个接口的泛型类

Question

I have a generic method which using multiple interfaces,

public T GetZonePrices<T>() where T : IRegionalZonePrice, INationalZonePrice, new()
{
// codes here
}

Then, I have a class that will be used to replace the T. It only implement one interface.

public class MarketRegionalZonePrice : IRegionalZonePrice
{
// properties here
}

How do you use the generic method by passing the class which only implemented one of the interfaces?

var result = GetZonePrices<MarketRegionalZonePrice>();

It gives me error,

"The type .. cannot be used as parameter type 'T' in the generic type or method .. . There is no implicit reference conversion from .. to .. ."

Answer 1

As mentioned in the comments, you can't.

What you could do though is:

public inteface IZonePrice 
{
// codes here
}
public interface IRegionalZonePrice : IZonePrice  
{
// codes here
}
public interface INationalZonePrice : IZonePrice 
{ 
// codes here
}

public T GetZonePrices<T>() where T :IZonePrice, new()
{
// codes here
}

Then this would work:

public class MarketRegionalZonePrice : IRegionalZonePrice
{
// properties here
}

...

var result = GetZonePrices<MarketRegionalZonePrice>()

if need be you can check the type of T with T is IRegionalZonePrice or T is INationalZonePrice

Is there much different between these interfaces? Because it almost looks to me that you overcomplicated your business model / logic?

You probably just need the interface IZonePrice and then your implementation will be public class RegionalZonePrice : IZonePrice and public class NationalZonePrice : IZonePrice with the respective different values for each Zone.