如何从字段的字符串名称访问案例类字段值 [英] How To Access access Case class field Value from String name of the field

问题描述

我应该如何从表示字段的给定字符串值中提取案例类的字段的值.

How should I extract the value of a field of a case class from a given String value representing the field.

例如:

case class Person(name: String, age: Int)
val a = Person("test",10)

现在给定一个字符串 name 或 age 我想从变量 a 中提取值.我该怎么做呢?我知道这可以使用反射来完成，但我不确定如何?

Now here given a string name or age i want to extract the value from variable a. How do i do this? I know this can be done using reflection but I am not exactly sure how?

推荐答案

使用 Shapeless 镜头可以实现您的需求.这也会在编译时而不是运行时将字段实际存在于案例类上的约束:

What you're looking for can be achieve using Shapeless lenses. This will also put the constraint that a field actually exists on a case class at compile time rather than run time:

import shapeless._

case class Person(name: String, age: Int)

val nameLens = lens[Person] >> 'name
val p = Person("myName", 25)

nameLens.get(p)

产量:

res0: String = myName

如果你试图提取一个不存在的字段，你会得到一个编译时错误，这是一个更有力的保证:

If you try to extract a non existing field, you get a compile time error, which is a much stronger guarantee:

import shapeless._

case class Person(name: String, age: Int)

val nonExistingLens = lens[Person] >> 'bla
val p = Person("myName", 25)

nonExistingLens.get(p)

编译器喊:

Error:(5, 44) could not find implicit value for parameter mkLens: shapeless.MkFieldLens[Person,Symbol with shapeless.tag.Tagged[String("bla")]]
val nonExistingLens = lens[Person] >> 'bla

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