我是Scala和SBT的新手。我在一个开源项目的build.sbt文件中注意到了一个不熟悉的运算符:
:=
以下是它的几个使用示例:
lazy val akkaApp = Project(id = "akka-app", base = file("akka-app"))
.settings(description := "Common Akka application stack: metrics, tracing, logging, and more.")
并且它在这个较大的代码片段中使用了几次:
lazy val jobServer = Project(id = "job-server", base = file("job-server"))
.settings(commonSettings)
.settings(revolverSettings)
.settings(assembly := null.asInstanceOf[File])
.settings(
description := "Spark as a Service: a RESTful job server for Apache Spark",
libraryDependencies ++= sparkDeps ++ slickDeps ++ cassandraDeps ++ securityDeps ++ coreTestDeps,
test in Test <<= (test in Test).dependsOn(packageBin in Compile in jobServerTestJar)
.dependsOn(clean in Compile in jobServerTestJar)
.dependsOn(buildPython in jobServerPython)
.dependsOn(clean in Compile in jobServerPython),
testOnly in Test <<= (testOnly in Test).dependsOn(packageBin in Compile in jobServerTestJar)
.dependsOn(clean in Compile in jobServerTestJar)
.dependsOn(buildPython in jobServerPython)
.dependsOn(clean in Compile in jobServerPython),
console in Compile <<= Defaults.consoleTask(fullClasspath in Compile, console in Compile),
fullClasspath in Compile <<= (fullClasspath in Compile).map { classpath =>
extraJarPaths ++ classpath
},
fork in Test := true
)
.settings(publishSettings)
.dependsOn(akkaApp, jobServerApi)
.disablePlugins(SbtScalariform)
我的最佳猜测是它的意思是“如果尚未声明,则声明它”。
:=
和=
是相同的,只是它会检查类型安全性。 - Sam Malayek:=
的行是“表达式,而不是语句”。这在Andrey的回答中得到了详细解释。 - Sam Malayek