阴影/删除字符串插值器

问题描述

我正在使用两个定义字符串插值器的库（为简化起见，简化了代码）：

Http4s：

implicit class LiteralsOps(val sc: StringContext) extends AnyVal {
  def uri(args: Any*): Uri = macro LiteralSyntaxMacros.uriInterpolator
  (...)
  def ipv4(args: Any*): Uri.Ipv4Address = macro LiteralSyntaxMacros.ipv4AddressInterpolator
  def ipv6(args: Any*): Uri.Ipv6Address = macro LiteralSyntaxMacros.ipv6AddressInterpolator
}

ip4s：

implicit class IpLiteralSyntax(val sc: StringContext) extends AnyVal {
  def ip(args: Any*): IpAddress = macro LiteralSyntaxMacros.ipInterpolator
  def ipv4(args: Any*): Ipv4Address = macro LiteralSyntaxMacros.ipv4Interpolator
  def ipv6(args: Any*): Ipv6Address = macro LiteralSyntaxMacros.ipv6Interpolator
  (...)
  def host(args: Any*): Hostname = macro LiteralSyntaxMacros.hostnameInterpolator
}

我想同时使用它们，即Http4s中的uri插值器和ip4s中的各种插值器。问题在于以下代码：

import com.comcast.ip4s._
import org.http4s.syntax.literals._

class Foo(cidr: Cidr[Ipv4Address] = ipv4"192.168.1.1" / 24)

无法编译：

[error] Note that implicit conversions are not applicable because they are ambiguous:
[error]  both method IpLiteralSyntax in package ip4s of type (sc: StringContext): com.comcast.ip4s.package.IpLiteralSyntax
[error]  and method http4sLiteralsSyntax in trait LiteralsSyntax of type (sc: StringContext): org.http4s.syntax.LiteralsOps
[error]  are possible conversion functions from StringContext to ?{def ipv4: ?}
[error]   class Foo(cidr: Cidr[Ipv4Address] = ipv4"192.168.1.1" / 24)

反正有没有从隐式作用域中隐藏/删除字符串插值器的方法？

解决方法

您的问题显然是ipv4和ipv6的插值器冲突，并且编译器不知道要使用哪个插值器。

冲突隐式问题可以通过为隐式之一提供更高的优先级来解决。这可以通过使用lower-priority implicits into a trait and then extend an object,that declares higher-priority implicits来完成。

来自http4s的隐含性可以带特征AllSyntax：

import com.comcast.ip4s._
import org.http4s.Uri
import org.http4s.syntax.AllSyntax

case class Foo(cidr: Cidr[Ipv4Address] = ipv4"192.168.1.1" / 24)

class MyApp extends AllSyntax {

  val testUri: Uri = uri"http://test.pl" //we can still use uri interpolator from http4s

}

但这仍然无法编译：

import org.http4s.Uri
import org.http4s.syntax.AllSyntax
import com.comcast.ip4s._

class MyApp extends AllSyntax {

  val testUri: Uri = uri"http://test.pl"
  val ip = ipv4"192.168.1.1" / 24 //compile error

}

不幸的是，ip4s没有提供任何将隐式函数引入范围的特征，因此我们可以对它们进行优先级排序。

您可以做的是创建另一个对象，在其中复制包对象com.comcast.ip4s的内部内容，然后扩展AllSyntax：

import org.http4s.Uri
import org.http4s.syntax.AllSyntax
import com.comcast.ip4s._
import scala.language.experimental.macros

object MySyntax extends AllSyntax {

  //copied from com.comcast.ip4s
  final implicit class IpLiteralSyntax(val sc: StringContext) extends AnyVal {
    def ip(args: Any*): IpAddress = macro LiteralSyntaxMacros.ipInterpolator
    def ipv4(args: Any*): Ipv4Address =
    macro LiteralSyntaxMacros.ipv4Interpolator
    def ipv6(args: Any*): Ipv6Address =
    macro LiteralSyntaxMacros.ipv6Interpolator
    (...)
  }

}

然后您可以像这样使用它：

class MyApp extends App {

  import MySyntax._

  val testUri: Uri = uri"http://test.pl"
  val ip = ipv4"192.168.1.1" / 24 //interpolator from com.comcast.ip4s has higher priority

}