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Swift泛型Protocol对比C俄罗斯贵宾会#泛型Interface

  本篇纯属抬杠之作,之前我们提到了Swift的泛型Protocol使用associatedtype关键字,而不是使用<Type>语法的泛型参数。这其中有什么好处呢?

  我就这个问题搜索了一些回答,大体上提到两点:

  <Type>语法对Protocol没有意义,Protocol仅需要定义一个抽象的概念,具体的类型应该由实现的Class来明确,比如:

ClassWithInt<Int>: NumberProtocol
ClassWithDouble<Double>: NumberProtocol

  associatedtype可以用来给Protocol中特定Func添加泛型约束,而不是限定整个Protocol

protocol GeneratorType {
    associatedtype Element
    public mutating func next() -> Self.Element?
}

  听上去还是有一定道理的,然后实践是检验事实的唯一标准。下面我们通过代码实例来和C#进行对比。首先拿出网上多被引用解释上述两个观点的Swift代码:

public protocol Automobile {
    associatedtype FuelType
    associatedtype ExhaustType
    func drive(fuel: FuelType) -> ExhaustType
}
public protocol Fuel {
    associatedtype ExhaustType
    func consume() -> ExhaustType
}
public protocol Exhaust {
    init()
    func emit()
}

public struct UnleadedGasoline<E: Exhaust>: Fuel {
    public func consume() -> E {
        print("...consuming unleaded gas...")
        return E()
    }
}
public struct CleanExhaust: Exhaust {
    public init() {}
    public func emit() {
        print("...this is some clean exhaust...")
    }
}
public class Car<F: Fuel,E: Exhaust>: Automobile where F.ExhaustType == E {
    public func drive(fuel: F) -> E {
        return fuel.consume()
    }
}

public class Car1<F: Fuel>: Automobile {
    public func drive(fuel: F) -> F.ExhaustType {
        return fuel.consume()
    }
}

  具体的使用情况如下:

var car = Car<UnleadedGasoline<CleanExhaust>, CleanExhaust>()
car.drive(fuel: UnleadedGasoline<CleanExhaust>()).emit()

var fusion = Car1<UnleadedGasoline<CleanExhaust>>()
fusion.drive(fuel: UnleadedGasoline<CleanExhaust>()).emit()

  转换成C#代码的话,有两种思路,首先是把泛型参数放到Interface层面:

    public interface Automobile<FuelType, ExhaustType>
    {
        ExhaustType Drive(FuelType fuel);
    }
    public interface Fuel<ExhaustType>
    {
        ExhaustType consume();
    }
    public interface Exhaust 
    {
        void Emit();
    }

    public class UnleadedGasoline<Exhaust> : Fuel<Exhaust> where Exhaust : new()
    {
        public Exhaust consume()
        {
            Console.WriteLine("...consuming unleaded gas...");
            return new Exhaust();
        }
    }
    public class CleanExhaust : Exhaust
    {
        public void Emit()
        {
            Console.WriteLine("...this is some clean exhaust...");
        }
    }
    public class Car : Automobile<UnleadedGasoline<CleanExhaust>, CleanExhaust>
    {
        public CleanExhaust Drive(UnleadedGasoline<CleanExhaust> fuel)
        {
            return fuel.consume();
        }
    }

  还可以模仿Swift对Automobile多做一层继承进行包装:

    public interface Car1<T1> : Automobile<UnleadedGasoline<T1>, T1> where T1 : new()
    {

    }

    public class SimpleCar : Car1<CleanExhaust>
    {
        public CleanExhaust Drive(UnleadedGasoline<CleanExhaust> fuel)
        {
            return fuel.consume();
        }
    }

调用的时候没有什么太大的差别:

  var gaso = new UnleadedGasoline<CleanExhaust>();
  var car = new Car();
  car.Drive(gaso).Emit();

  var simpleCar = new SimpleCar();
  simpleCar.Drive(gaso).Emit();

  和Swift比较不同的是,我们在Interface就代入了泛型参数。但是由于我们不能直接实例化Interface,所以并不能直接使用Automobile来减少一层继承关系。

  因为上述提到的使用associatedtype 的第一点理由见仁见智,这里不分高下。

  C#还有第二种思路,就是我也把泛型约束下放到Func层级:

    public interface Automobile
    {
        ExhaustType Drive<FuelType,ExhaustType>(FuelType fuel) where ExhaustType : new();
    }
    public interface Fuel
    {
        ExhaustType consume<ExhaustType>() where ExhaustType : new();
    }

    public class UnleadedGasoline : Fuel
    {
        public Exhaust consume<Exhaust>() where Exhaust : new()
        {
            Console.WriteLine("...consuming unleaded gas...");
            return new Exhaust();
        }
    }

    public class Car2 : Automobile
    {
        public CleanExhaust Drive<UnleadedGasoline, CleanExhaust>(UnleadedGasoline fuel) where CleanExhaust : new()
        {
            return  (fuel as Fuel).consume<CleanExhaust>();
        }
    }

C#的接口并不能定义构造函数。强行模仿起来还真是有点累啊。最终的使用也很简单:

    var fuel = new UnleadedGasoline();
    var car2 = new Car2();
    car2.Drive<UnleadedGasoline,CleanExhaust>(fuel).Emit();

俄罗斯贵宾会,  通篇比较下来,应该说Swift通过associatedtype 关键字和<Type>的混用,使得泛型的定义更为复杂也更灵活了。

  GitHub:

https://github.com/manupstairs/LearnSwift

https://github.com/manupstairs/LearnDotNetCore

 

 

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