使用通用方法將介面作為約束型別

這是一個如何在類 Animal 上使用通用型別 TFood 的示例

public interface IFood
{
    void EatenBy(Animal animal);
}

public class Grass: IFood
{
    public void EatenBy(Animal animal)
    {
        Console.WriteLine("Grass was eaten by: {0}", animal.Name);
    }
}

public class Animal
{
    public string Name { get; set; }

    public void Eat<TFood>(TFood food)
        where TFood : IFood
    {
        food.EatenBy(this);
    }
}

public class Carnivore : Animal
{
    public Carnivore()
    {
        Name = "Carnivore";
    }
}

public class Herbivore : Animal, IFood
{
    public Herbivore()
    {
        Name = "Herbivore";
    }
    
    public void EatenBy(Animal animal)
    {
        Console.WriteLine("Herbivore was eaten by: {0}", animal.Name);
    }
}

你可以像這樣呼叫 Eat 方法：

var grass = new Grass();        
var sheep = new Herbivore();
var lion = new Carnivore();
    
sheep.Eat(grass);
//Output: Grass was eaten by: Herbivore

lion.Eat(sheep);
//Output: Herbivore was eaten by: Carnivore

在這種情況下，如果你嘗試呼叫：

sheep.Eat(lion);

這是不可能的，因為物件獅子沒有實現介面 IFood。嘗試進行上述呼叫將生成編譯器錯誤：“型別’食肉動物’不能在泛型型別或方法’Animal.Eat(TFood)‘中用作型別引數’TFood’。沒有隱式引用轉換’ Carnivore’到’IFood’。“