英文:
Is there a way to define an indexable type in golang?
问题
我最近发现了一个通过直接索引（即graph[key]）进行图处理的库。我有一个节点树，其中的子节点位于特定属性node.childs[key]下面。
我想知道是否有一种方法可以定义一种类型，以便通过直接键映射来访问属性，例如node[key]将映射到node.childs[key]。在定义新类型时是否有实现这一点的方法？
英文:
I recently came across a library that does graph processing by direct indexing i.e graph[key], I have a node tree which has its child nodes under a certain attribute node.childs[key].
I was wondering if there is a way to define a type so that an attribute could be accessible through direct key mapping, such as node[key] would be mapped to node.childs[key]. Is there a way to achieve this while defining new types?
答案1
得分: 5
不，你想要的是不可能的。规范不允许这样做。规范：索引表达式：
> 形式为
>
> a[x]
>
> 的主表达式表示数组、指向数组的指针、切片、字符串或映射 a 中由 x 索引的元素。值 x 分别称为 索引 或 映射键。以下规则适用：
>
> 对于 数组类型 A 的 a：[...]
>
> 对于指向数组类型的 a：[...]
>
> 对于 切片类型 S 的 a：[...]
>
> 对于 字符串类型 的 a：[...]
>
> 对于 映射类型 M 的 a：[...]
>
> 对于 类型参数类型 P 的 a：[...]
>
> 否则，a[x] 是非法的。
只有列出的这些类型可以进行索引，其他类型都不行。而且你甚至不能改变索引运算符的含义（无法重载它）。
英文:
No, it's not possible to do what you want. The spec does not allow it. Spec: Index expressions:
> A primary expression of the form
>
> a[x]
>
> denotes the element of the array, pointer to array, slice, string or map a indexed by x. The value x is called the index or map key, respectively. The following rules apply:
>
> For a of array type A: [...]
>
> For a of pointer to array type: [...]
>
> For a of slice type S: [...]
>
> For a of string type: [...]
>
> For a of map type M: [...]
>
> For a of type parameter type P: [...]
>
> Otherwise a[x] is illegal.
Only these listed types are indexable, no other. And you can't even change the meaning of the index operator (you can't override it).
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