给出以下宏（感谢@TravisBrown提供此帮助 ）：
JetDim.scala
case class JetDim(dimension: Int) { require(dimension > 0) } object JetDim { def validate(dimension: Int): Int = macro JetDimMacro.apply def build(dimension: Int): JetDim = JetDim(validate(dimension)) }JetDimMacro.scala
import reflect.macros.Context object JetDimMacro { sealed trait PosIntCheckResult case class LteqZero(x: Int) extends PosIntCheckResult case object NotConstant extends PosIntCheckResult def apply(c: Context)(dimension: c.Expr[Int]): c.Expr[Int] = { import c.universe._ getInt(c)(dimension) match { case Right(_) => reify { dimension.splice } case Left(LteqZero(x)) => c.abort(c.enclosingPosition, s"$x must be > 0.") case Left(NotConstant) => reify { dimension.splice } } } def getInt(c: Context)(dimension: c.Expr[Int]): Either[PosIntCheckResult, Int] = { import c.universe._ dimension.tree match { case Literal(Constant(x: Int)) => if (x > 0) Right(x) else Left(LteqZero(x)) case _ => Left(NotConstant) } } }它适用于REPL：
scala> import spire.math.JetDim import spire.math.JetDim scala> JetDim.validate(-55) <console>:9: error: -55 must be > 0. JetDim.validate(-55) ^ scala> JetDim.validate(100) res1: Int = 100但是，我想将这个编译时检查（通过JetDimMacro ） JetDimMacro到case类的apply方法中。
尝试1
case class JetDim(dimension: Int) { require(dimension > 0) } object JetDim { private def validate(dimension: Int): Int = macro JetDimMacro.apply def build(dimension: Int): JetDim = JetDim(validate(dimension)) }但那失败了：
scala> import spire.math.JetDim import spire.math.JetDim scala> JetDim.build(-55) java.lang.IllegalArgumentException: requirement failed at scala.Predef$.require(Predef.scala:207) at spire.math.JetDim.<init>(Jet.scala:21) at spire.math.JetDim$.build(Jet.scala:26) ... 43 elided尝试2
class JetDim(dim: Int) { require(dim > 0) def dimension: Int = dim } object JetDim { private def validate(dimension: Int): Int = macro JetDimMacro.apply def apply(dimension: Int): JetDim = { validate(dimension) new JetDim(dimension) } }然而那也失败了：
scala> import spire.math.JetDim import spire.math.JetDim scala> JetDim(555) res0: spire.math.JetDim = spire.math.JetDim@4b56f205 scala> JetDim(-555) java.lang.IllegalArgumentException: requirement failed at scala.Predef$.require(Predef.scala:207) at spire.math.JetDim.<init>(Jet.scala:21) at spire.math.JetDim$.apply(Jet.scala:30) ... 43 elided我想修改JetDimMacro#apply来返回JetDim而不是Int 。 但是， JetDim存在于core项目中，从我看来，这取决于macros项目（ JetDimMacro所在的JetDimMacro ）。
如何在JetDim的伴随对象中使用此validate方法在编译时检查正int？
Given the following macro (thanks @TravisBrown for this help ):
JetDim.scala
case class JetDim(dimension: Int) { require(dimension > 0) } object JetDim { def validate(dimension: Int): Int = macro JetDimMacro.apply def build(dimension: Int): JetDim = JetDim(validate(dimension)) }JetDimMacro.scala
import reflect.macros.Context object JetDimMacro { sealed trait PosIntCheckResult case class LteqZero(x: Int) extends PosIntCheckResult case object NotConstant extends PosIntCheckResult def apply(c: Context)(dimension: c.Expr[Int]): c.Expr[Int] = { import c.universe._ getInt(c)(dimension) match { case Right(_) => reify { dimension.splice } case Left(LteqZero(x)) => c.abort(c.enclosingPosition, s"$x must be > 0.") case Left(NotConstant) => reify { dimension.splice } } } def getInt(c: Context)(dimension: c.Expr[Int]): Either[PosIntCheckResult, Int] = { import c.universe._ dimension.tree match { case Literal(Constant(x: Int)) => if (x > 0) Right(x) else Left(LteqZero(x)) case _ => Left(NotConstant) } } }It works from the REPL:
scala> import spire.math.JetDim import spire.math.JetDim scala> JetDim.validate(-55) <console>:9: error: -55 must be > 0. JetDim.validate(-55) ^ scala> JetDim.validate(100) res1: Int = 100But, I'd like to build this compile-time check (via the JetDimMacro) into the case class's apply method.
Attempt 1
case class JetDim(dimension: Int) { require(dimension > 0) } object JetDim { private def validate(dimension: Int): Int = macro JetDimMacro.apply def build(dimension: Int): JetDim = JetDim(validate(dimension)) }But that failed:
scala> import spire.math.JetDim import spire.math.JetDim scala> JetDim.build(-55) java.lang.IllegalArgumentException: requirement failed at scala.Predef$.require(Predef.scala:207) at spire.math.JetDim.<init>(Jet.scala:21) at spire.math.JetDim$.build(Jet.scala:26) ... 43 elidedAttempt 2
class JetDim(dim: Int) { require(dim > 0) def dimension: Int = dim } object JetDim { private def validate(dimension: Int): Int = macro JetDimMacro.apply def apply(dimension: Int): JetDim = { validate(dimension) new JetDim(dimension) } }Yet that failed too:
scala> import spire.math.JetDim import spire.math.JetDim scala> JetDim(555) res0: spire.math.JetDim = spire.math.JetDim@4b56f205 scala> JetDim(-555) java.lang.IllegalArgumentException: requirement failed at scala.Predef$.require(Predef.scala:207) at spire.math.JetDim.<init>(Jet.scala:21) at spire.math.JetDim$.apply(Jet.scala:30) ... 43 elidedI thought to modify JetDimMacro#apply to return a JetDim rather than an Int. However, JetDim lives in the core project, which, from what I see, depends on the macros project (where JetDimMacro lives).
How can I use this validate method from JetDim's companion object to check for positive int's at compile-time?
最满意答案
问题是，当我们在apply调用validate ，我们不再处理常量 （单例类型）。 因此，validate获得一个非常数Int。
作为替代方案，您可以尝试使用隐式见证进行正向整数，然后JetDim将其作为构造函数。 例如，类似于：
package com.example case class JetDim(n: PositiveInt) case class PositiveInt(value: Int) { require(value > 0) }然后，我们从Int => PositiveInt中添加一个隐式（宏）转换来进行检查。
import scala.language.experimental.macros import scala.reflect.macros.blackbox.Context object PositiveInt { implicit def wrapConstantInt(n: Int): PositiveInt = macro verifyPositiveInt def verifyPositiveInt(c: Context)(n: c.Expr[Int]): c.Expr[PositiveInt] = { import c.universe._ val tree = n.tree match { case Literal(Constant(x: Int)) if x > 0 => q"_root_.com.example.PositiveInt($n)" case Literal(Constant(x: Int)) => c.abort(c.enclosingPosition, s"$x <= 0") case x => c.abort(c.enclosingPosition, s"cannot verify $x > 0") } c.Expr(tree) } }然后，您可以使用将传递的JetDim(-12)或将失败的JetDim(-12) （宏将Int扩展为PositiveInt）。
The problem is that by the time we call validate in apply we are no longer dealing with a constant (singleton type). So, validate gets a non-constant Int.
As an alternative, you could try using an implicit witness for positive ints, which JetDim then takes as a constructor. For instance, something like:
package com.example case class JetDim(n: PositiveInt) case class PositiveInt(value: Int) { require(value > 0) }Then, we add an implicit (macro) conversion from Int => PositiveInt that does your check.
import scala.language.experimental.macros import scala.reflect.macros.blackbox.Context object PositiveInt { implicit def wrapConstantInt(n: Int): PositiveInt = macro verifyPositiveInt def verifyPositiveInt(c: Context)(n: c.Expr[Int]): c.Expr[PositiveInt] = { import c.universe._ val tree = n.tree match { case Literal(Constant(x: Int)) if x > 0 => q"_root_.com.example.PositiveInt($n)" case Literal(Constant(x: Int)) => c.abort(c.enclosingPosition, s"$x <= 0") case x => c.abort(c.enclosingPosition, s"cannot verify $x > 0") } c.Expr(tree) } }You can then use JetDim(12), which will pass, or JetDim(-12), which will fail (the macro expands the Int to a PositiveInt).
更多推荐
发布评论