是否有任何技术上的原因,导致C#要求所有泛型类型参数都必须用它们所在类的名称进行声明?
例如,我想声明这个:
public class FruitCollection<TFruit> : FoodCollection<TFoodGroup>
where TFruit : IFood<TFoodGroup>
where TFoodGroup : IFoodGroup { }
public class AppleCollection : FruitCollection<Apple> { }
public class TomatoCollection : FruitCollection<Tomato> { }
TFruit
是一个IFood<TFoodGroup>
,因此如果提供了TFruit
,就必须定义TFoodGroup
,即使我没有明确声明。
相反,我必须这样做:
public class FruitCollection<TFoodGroup, TFruit> : FoodCollection<TFoodGroup>
where TFruit : IFood<TFoodGroup>
where TFoodGroup : IFoodGroup { }
// Anything other than FruitGroup is an error when combined with Apple
public class AppleCollection : FruitCollection<FruitGroup, Apple> { }
// Anything other than VegetableGroup is an error when combined with Tomato
public class TomatoCollection : FruitCollection<VegetableGroup, Tomato> { }
第二种方法可以很好地工作,并防止任何无效的组合编译,但随着越来越多不必要的泛型类型声明添加到参数列表中,它变得混乱起来。
集合中的其他定义为:
public interface IFoodGroup { }
public class FruitGroup : IFoodGroup { }
public class VegetableGroup : IFoodGroup { }
public interface IFood<TFoodGroup> where TFoodGroup : IFoodGroup { }
public class Apple : IFood<FruitGroup> { }
public class Tomato : IFood<VegetableGroup> { }
public abstract class FoodCollection<TFoodGroup> where TFoodGroup : IFoodGroup { }