检查无形中可扩展记录之间的子类型关系

问题描述

我有两个无形的可扩展记录，person 和 employee.employee 记录在某种意义上是 person 的子类型，因为它具有 person 所做的所有字段，并且这些字段都是person 中对应的字段:

I have two shapeless extensible records, person and employee. The employee record is a subtype of person in some sense because it has all of the fields that person does and those fields are all subtypes of the corresponding fields in person:

import shapeless._ ; import syntax.singleton._ ; import record._

val employeeId = ("first name" ->> "Jane") :: ("last name" ->> "Doe") :: ("title" ->> "software engineer") :: HNil

val employee =
      ("id" ->> employeeId) ::
      ("city" ->> "San Francisco") ::
      ("company" ->> "Generic Inc.") ::
      HNil

val personId = ("first name" ->> "Jane") :: ("last name" ->> "Doe") :: HNil

val person =
      ("id" ->> personId) ::
      ("city" ->> "San Francisco") ::
      HNil

如何检查一个记录是否是另一个记录的子类型?我希望能够在编译时和运行时执行此操作.我想到的一个用例是，我想静态验证函数不会从记录中删除任何字段.所以我的函数可以接受一个 person 并将其转换为一个 employee 但如果它删除了city"或id"字段，程序就不应该编译.

How can I check if one record is a subtype of another? I want to be able to do this both at compile time and at runtime. One use-case I have in mind is that I want to statically verify that a function doesn't remove any fields from a record. So my function could take a person and transform it into an employee but if it dropped the "city" or "id" fields the program should not compile.

我还希望能够比较 employee 和 person 的共享组件.我想将两个对象都视为 person 并检查它们是否相等.我该怎么做?

I also want to be able to compare the shared components of employee and person. I want to view both objects as just persons and check them for equality. How can I do this?

推荐答案

• 如何检查一个记录是否是另一个记录的子类型?

您可以查看此 repo 中的 Extractor 类型类.它实现了深度和宽度子类型.

You may look at the Extractor type class in this repo. It implements both depth and width subtyping.

https://github.com/eugengarkusha/RecordsDeepMerge

• 我希望能够在编译时和运行时执行此操作

子类型关系在编译时可见.使用 Extractor 类型类(来自提到的 repo)从子记录中获取超级记录的所有字段.

Subtyping relation is witnessed in compile time.Use the Extractor type class(from mentioned repo) to get all fields of super-record from sub-record.

• 我还希望能够比较员工和人员的共享组成部分.我想将两个对象都视为人并检查它们是否相等.我该怎么做?

(使用来自上述 repo 的代码):

(using the code from mentioned repo):

 type PersonId = Record.`"first name" ->String, "last name" ->String`.T
 type Person = Record.`"id" -> PersonId, "city" -> String`.T
 employee1.deepExtract[Person] == employee2.deepExtract[Person]

• 我想静态验证函数不会从记录中删除任何字段.所以我的函数可以接受一个人并将其转换为员工，但如果它删除了city"或id"字段，程序就不应编译.

在这种情况下不需要子类型检查:

no subtype checks are needed in this case:

def personToEmployee(p: Person): Employee = ???

类型检查器不会让您删除城市或 ID 字段

type checker won't let you remove city or id fields

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