使用宏，如何获取结构字段的唯一名称? [英] Using macros, how to get unique names for struct fields?

问题描述

假设我这样调用了一些宏:

Suppose I have some macro invoked as such:

my_macro!(Blah, (a, b, c));

它会输出如下内容:

struct Blah {
    a: i32,
    b: i32,
    c: i32
}
impl Blah {
    fn foo() -> i32 {
        a + b + c
    }
}

(人工示例)

这些字段对结构是私有的，但是我需要允许重新定义.因此，输入

These fields will be private to the struct, but I need to allow redefinitions. So, the input

my_macro!(Blah, (a, b, c, a));

将生成类似以下内容的

struct Blah {
    a1: i32,
    b: i32,
    c: i32,
    a2: i32
}
impl Blah {
    fn foo() -> i32 {
        a1 + b + c + a2
    }
}

命名方案不需要遵循任何逻辑模式.

The naming scheme doesn't need to follow any logical pattern.

这可能吗?

推荐答案

如果不使用编译器插件，不，我认为这是不可能的.两个原因:

Without using a compiler plugin, no, I don't believe this is possible. Two reasons:

1. 您不能构造标识符.有concat_idents!，但是由于扩展宏的方式，在这种情况下它没有用.

1. You can't construct identifiers. There's concat_idents!, but due to the way macros are expanded, it's useless in this situation.

您不能进行非文字比较.也就是说，无法通过宏解决以前已经在a中看到过一次的问题.

You can't do non-literal comparisons. That is, there's no way of the macro working out that it's already seen a once before.

关于获得的最接近的结果是完全替换所有提供的标识符，并使用固定的标识符列表，但这可能不是您想要的；在这种情况下，只需要指定4个字段并生成固定大小的数组[i32; 4]会更容易.

About the closest you could get is to just outright replace all the provided identifiers with a fixed list of identifiers, but that's probably not what you want; in that case, it'd be easier to just specify that you want 4 fields, and generate a fixed-size array [i32; 4].

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