Eiffel：有没有办法在没有任何附加实例的情况下测试 Class 的给定通用参数？

Question

有没有办法在没有任何附加实例的情况下测试 Class 的给定通用参数？

class BAG[G -> MOUSE]

feature -- 

    discriminate
        do
            if G.conforms_to (MAMMAL) then
                io.putstring ("you gave me a real animal")
            elseif G.conforms_to (COMPUTER_ACCESSORY) then
                io.putstring ("Seems you don't like animals such as computers")
            else
                io.pustring ("Still dont know what you are dealing with")
            end
        end

Answer 1

您几乎成功了。缺少的部分是大括号和圆括号：

        if ({G}).conforms_to ({MAMMAL}) then
            io.put_string ("You gave me a real animal.")
        elseif ({G}).conforms_to ({COMPUTER_ACCESSORY}) then
            io.put_string ("Seems you don't like animals such as computers.")
        else
            io.put_string ("Still don't know what you are dealing with.")
        end

解释：

{FOO}，其中FOO是类型名，代表类型对象。它适用于任何类型，包括形式泛型，因此 {G} 和 {MAMMAL}.
语法{FOO}.bar是为非对象调用保留的。但是这里我们想要对类型对象进行对象调用。因此，{G} 被括在括号中：({G}).conforms_to（而不是 {G}.conforms_to）。

Eiffel：有没有办法在没有任何附加实例的情况下测试 Class 的给定通用参数？

Eiffel: Is there a way to test a given Generic parameter of a Class without any attached instance of it?

eiffel

generic-programming