generics - Ada 通用包扩展

Question

我有一个通用包Containers.Stacks，看起来大致像

generic
    type Value_Type is private;
package Containers.Stacks with Preelaborate is

    --Node stuff

    type Stack is new Container with private;

    --Other Stack stuff
    --Private stuff
end Containers.Stacks;

一切(似乎)都运行得很好。我想重用此实现来创建扩展但用途更窄的堆栈。我提出了以下建议:

with Containers.Stacks;

generic
    type Value_Type is range <>;
package Containers.Integer_Stacks with Preelaborate is

    package Stacks is new Containers.Stacks(Value_Type);
    use Stacks;

    type Stack is new Stacks.Stack with null record;

    procedure Add(Self : in out Stack);

    procedure Subtract(Self : in out Stack);

    --So on

end Containers.Integer_Stacks;

重点是，我不想只为特定的整数堆栈重新实现所有常见的堆栈内容。这可行，但留下了 Containers.Integer_Stacks.Stack 和 Containers.Integer_Stacks.Stacks.Stack 的丑陋和奇怪的困惑，我想避免这种情况。然而，尝试将包初始化放在私有(private)部分中也会隐藏所有子例程。是否有更合适的方法来完成我想要做的事情，或者用户是否必须处理存在的同级包初始化？

替代方法:我发现可以定义一个名为 Containers.Stacks.Integer 的 Containers.Stacks 子包，如下所示:

generic
    with function "+"(Left, Right: Value_type) return Value_Type is <>;
package Containers.Stacks.Integer is
    procedure Add(Self : in out Stack);
end Containers.Stacks.Integer;

这有效。只是现在我无法调用 Stack.Add，我被迫调用 Add(Stack)。

Answer 1

你可以看看

with Containers.Stacks;
generic
   type Value_Type is range <>;
   with package Basis_Stack is new Containers.Stacks (Value_Type => Value_Type);
package Containers.Integer_Stacks with Preelaborate is
   type Stack is new Basis_Stack.Stack with private;
...

这确实需要您的用户自己适本地实例化 Containers.Stacks。