[英]scala: using method of extending class based on macros invokes trait default impl if type of instance is statically the base class
I have a trait T, I implement it with macro in class C. i create an instance of C and invoke its methods.我有一个特征 T,我在类 C 中用宏实现它。我创建了一个 C 的实例并调用它的方法。 if the type of the val containing an instance of C is C - works as expected.如果包含 C 实例的 val 的类型是 C - 按预期工作。 if the type of the val containing an instance of C is T - invokes methods as if T.如果包含 C 实例的 val 的类型是 T - 就像 T 一样调用方法。
best way to describe it that i can come up with is "virtual table broken" in scala-macros, but i don't know if that's a thing...我能想到的最好的描述方法是 Scala 宏中的“虚拟表损坏”,但我不知道这是否是一回事......
example code:示例代码:
Type in expressions for evaluation. Or try :help.
scala>
scala>
scala> import language.experimental.macros
import language.experimental.macros
scala>
scala>
scala> trait T { def doSomething(): Unit = println ("trait") }
defined trait T
scala>
scala>
scala> import scala.reflect.macros.Context
import scala.reflect.macros.Context
scala>
scala>
scala> object Macro {
| def doSomething(c: Context)(): c.universe.Tree = {
| import c.universe._
| q"""println ("macro")"""
| }
| }
warning: there was one deprecation warning (since 2.11.0); for details, enable `:setting -deprecation' or `:replay -deprecation'
defined object Macro
scala>
scala>
scala> class C extends T { override def doSomething(): Unit = macro Macro.doSomething }
defined class C
scala>
scala> val c: C = new C()
c: C = C@3bd1883a
scala> c.doSomething()
macro
scala>
scala> val t: T = new C()
t: T = C@4079fec7
scala> t.doSomething()
trait
Def macros are expanded at compile time so late binding / dynamic dispatch (which is a runtime feature) is impossible for them. def 宏在编译时被扩展,因此后期绑定/动态调度(这是一个运行时特性)对它们来说是不可能的。
At compile time it's unknown that t
has type C
, at compile time it's only known that t
has type T
.在编译时不知道t
类型为C
,在编译时只知道t
类型为T
。
See details here: Eugene Burmako.在此处查看详细信息:Eugene Burmako。 Unification of Compile-Time and Runtime Metaprogramming in Scalahttps://infoscience.epfl.ch/record/226166/files/EPFL_TH7159.pdf p. Scala 中编译时和运行时元编程的统一https://infoscience.epfl.ch/record/226166/files/EPFL_TH7159.pdf p。 98, §4.6.1 "Inheritance" 98, §4.6.1 “继承”
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