[英]Type-safe usage of Java reflection in Scala
I am trying to use Java reflection to replace the value for an object's field at runtime, but in a type-safe way.我正在尝试使用 Java 反射在运行时替换对象字段的值,但以类型安全的方式。
Let's assume we have the following object.假设我们有以下对象。
import cats.Eval
object Foo {
val bar: Eval[Int] = Eval.later(throw new Exception)
}
We want to change the value for Foo.bar
at runtime.我们想在运行时更改Foo.bar
的值。 We can easily define the following method using normal Java reflection:我们可以使用普通的 Java 反射轻松定义以下方法:
import java.lang.reflect.Field
def usingJavaReflection[T](targetObject: AnyRef, fieldName: String)(newValue: T): Unit = {
val field = targetObject.getClass.getDeclaredField(fieldName)
field.setAccessible(true)
field.set(targetObject, newValue)
}
// usage
usingJavaReflection(Foo, "bar")(Eval.now(42))
Now the question becomes: how to do that in a more type-safe way?现在问题变成了:如何以更类型安全的方式做到这一点?
def usingJavaReflectionButTypesafe[T](field: T)(newValue: T): Unit = ???
// intended usage
usingJavaReflectionButTypesafe(Foo.bar)(Eval.now(42))
This means being able to do a few things:这意味着能够做一些事情:
Foo.bar
should not be evaluated Foo.bar
不应该被评估Foo.bar
should be broken down into a target object Foo
and a field "bar"
相反,应该将Foo.bar
分解为目标对象Foo
和字段"bar"
Foo.bar
should be the same as for newValue
Foo.bar
的类型应该与newValue
的类型相同Bonus question: If this is possible, how to make it work for Scala 2.11 and 2.12 and 2.13.额外问题:如果可能,如何使其适用于 Scala 2.11、2.12 和 2.13。 I just cannot wrap my head around which Scala macros techniques are safe to use in which versions of Scala, and how.我无法确定哪些 Scala 宏技术可以安全地用于哪些 Scala 版本以及如何使用。
Try尝试
def usingJavaReflectionButTypesafe[T](field: => T)(newValue: T): Unit = macro impl[T]
def impl[T: c.WeakTypeTag](c: blackbox.Context)(field: c.Tree)(newValue: c.Tree): c.Tree = {
import c.universe._
field match {
case q"$expr.$tname" =>
q"usingJavaReflection($expr, ${tname.toString})($newValue)"
}
}
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