scala – 方法“|”中的预期类型的??解析器
发布时间:2020-12-16 18:07:18 所属栏目:安全 来源:网络整理
导读:我有针对 scala 2.8.0编译的以下代码: import scala.util.parsing.combinator.{syntactical,PackratParsers}import syntactical.StandardTokenParsersobject MyParser extends StandardTokenParsers with PackratParsers{ lexical.reserved ++= Set("int","
我有针对
scala 2.8.0编译的以下代码:
import scala.util.parsing.combinator.{syntactical,PackratParsers} import syntactical.StandardTokenParsers object MyParser extends StandardTokenParsers with PackratParsers{ lexical.reserved ++= Set("int","char","boolean") lazy val primitiveType:PackratParser[PrimitiveType[_]] = primitiveChar | primitiveInt | primitiveBool lazy val primitiveInt:PackratParser[PrimitiveType[Int]] = "int" ^^ { _ => PrimitiveType[Int]() } lazy val primitiveChar:PackratParser[PrimitiveType[Char]] = "char" ^^ { _ => PrimitiveType[Char]() } lazy val primitiveBool:PackratParser[PrimitiveType[Boolean]] = "boolean" ^^ { _ => PrimitiveType[Boolean]() } } object MyParser2 extends StandardTokenParsers with PackratParsers{ lexical.reserved ++= Set("int","boolean") lazy val primitiveType:PackratParser[PrimitiveType[_]] = primitiveChar | primitiveIntOrBool lazy val primitiveIntOrBool:PackratParser[PrimitiveType[_]] = "int" ^^ { _ => PrimitiveType[Int]() } | "boolean" ^^ {_ => PrimitiveType[Boolean]()} lazy val primitiveChar:PackratParser[PrimitiveType[Char]] = "char" ^^ { _ => PrimitiveType[Char]()} } case class PrimitiveType[T]() 编译MyParser1给出: error: inferred type arguments [this.PrimitiveType[_ >: _1 with Boolean <: AnyVal]] do not conform to method |'s type parameter bounds [U >: this.PrimitiveType[_ >: Char with Int <: AnyVal]] 我相信它因为|而失败了方法类型签名,定义为: def | [U >: T](q: => Parser[U]): Parser[U] 为什么U必须是T的超类型?什么应该是“primitiveType”的返回值? 解决方法
您需要将最后一行更改为
case class PrimitiveType[+T]() 这允许PrimitiveType [Int]< ;: PrimitiveType [AnyVal],当您想通过|合并PrimitiveType [Boolean]和PrimitiveType [Int]解析器的结果时需要它. 顺便说一句,我也建议写 PrimitiveType[AnyVal] 代替 PrimitiveType[_] 因为在你的情况下这更精确. (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |