scala

问题 I have a Slick query with two left joins (which end up as a Rep[Option[...]] ) and column maps. I need to filter (using like ) on the results. A row has to be included in the results if any of three columns match the like criteria, so I can't pre-filter the tables - I have to filter the resulting join, Rep[Option] s and all. I can't figure how to filter the Rep[Option[String]] columns. The below code does not compile due to "cannot resolve symbol ||" - if compiles perfectly when I remove the

问题 How can I specify the Scala version in a Gradle Scala project? The official documentation states that the scala-library dependency is used to get hold of the compiler. dependencies { compile 'org.scala-lang:scala-library:2.11.1' } Does this mean that Scala 2.11.1 will be used? 回答1: Specify the Scala library in the dependencies like so: dependencies { compile 'org.scala-lang:scala-library:2.11.1' } 来源： https://stackoverflow.com/questions/44374472/gradle-scala-plugin-how-to-specify-scala

问题 How can I specify the Scala version in a Gradle Scala project? The official documentation states that the scala-library dependency is used to get hold of the compiler. dependencies { compile 'org.scala-lang:scala-library:2.11.1' } Does this mean that Scala 2.11.1 will be used? 回答1: Specify the Scala library in the dependencies like so: dependencies { compile 'org.scala-lang:scala-library:2.11.1' } 来源： https://stackoverflow.com/questions/44374472/gradle-scala-plugin-how-to-specify-scala

问题 With Scala 2.13.x, I am getting scala.MatchError: null when I use a placeholder for an unused variable: scala> object Test { | val _: Any = null | } object Test scala> Test scala.MatchError: null ... 41 elided But with Scala 2.12.x, I am not getting scala.MatchError: null : scala> object Test { | val _: Any = null | } defined object Test scala> Test res1: Test.type = Test$@784c5ef5 Any reason? 回答1: As stated in scala 2.13 release notes: Underscore is no longer a legal identifier unless

问题 I have an issue where I have to calculate a column using a formula that uses the value from the calculation done in the previous row. I am unable to figure it out using withColumn API. I need to calculate a new column, using the formula: MovingRate = MonthlyRate + (0.7 * MovingRatePrevious) ... where the MovingRatePrevious is the MovingRate of the prior row. For month 1, I have the value so I do not need to re-calculate that but I need that value to be able to calculate the subsequent rows. I

问题 I need to cross-build a project with both Scala 2.10 and 2.11 (and ultimately 2.12 also). Some packages that were part of 2.10, for example parser-combinators, are packaged independently in 2.11. Thus they are not required to be mentioned in the 2.10 build but are required in 2.11. Furthermore, there may be more than one such package, which are required to use a common version. I found the documentation re: cross-building on the SBT site to be somewhat lacking in helpfulness here. And,

问题 This question already has an answer here : What are Scala context and view bounds? (1 answer) Closed 15 days ago . In specs2 there is a method called Around, documented here that has the following example: object http extends Around { def around[T <% Result](t: =>T) = openHttpSession("test") { t // execute t inside a http session } } The source for this code can be found here. I'm curious what the <% operator means in this context? EDIT: here is a solid answer on this subject, What are Scala

问题 This question already has an answer here : What are Scala context and view bounds? (1 answer) Closed 15 days ago . In specs2 there is a method called Around, documented here that has the following example: object http extends Around { def around[T <% Result](t: =>T) = openHttpSession("test") { t // execute t inside a http session } } The source for this code can be found here. I'm curious what the <% operator means in this context? EDIT: here is a solid answer on this subject, What are Scala

问题 This question already has an answer here : What are Scala context and view bounds? (1 answer) Closed 15 days ago . In specs2 there is a method called Around, documented here that has the following example: object http extends Around { def around[T <% Result](t: =>T) = openHttpSession("test") { t // execute t inside a http session } } The source for this code can be found here. I'm curious what the <% operator means in this context? EDIT: here is a solid answer on this subject, What are Scala

问题 In the REPL, I'm writing out the examples from Reflection - TypeTags and Manifests. I'm confused by the difference between WeakTypeTag and TypeTag . scala> import scala.reflect.runtime.universe._ import scala.reflect.runtime.universe._ TypeTag scala> def paramInfo[T](x: T)(implicit tag: TypeTag[T]): Unit = { | val targs = tag.tpe match { case TypeRef(_, _, args) => args } | println(s"type tag of $x has type arguments $targs") | } paramInfo: [T](x: T)(implicit tag: reflect.runtime.universe