An annotation for methods whose bodies may be excluded from compiler-generated bytecode.
Behavior is influenced by passing-Xelide-below <arg> toscalac. Calls to methods marked elidable (as well as the method body) will be omitted from generated code if the priority given the annotation is lower than that given on the command line.
@elidable(123) // annotation priorityscalac -Xelide-below 456 // command line priorityThe method call will be replaced with an expression which depends on the type of the elided expression. In decreasing order of precedence:
Unit ()Boolean falseT <: AnyVal 0T >: Null nullT >: Nothing Predef.???Complete example:
import scala.annotation._, elidable._object Test extends App { def expensiveComputation(): Int = { Thread.sleep(1000) ; 172 } @elidable(WARNING) def warning(msg: String) = println(msg) @elidable(FINE) def debug(msg: String) = println(msg) @elidable(FINE) def computedValue = expensiveComputation() warning("Warning! Danger! Warning!") debug("Debug! Danger! Debug!") println("I computed a value: " + computedValue)}% scalac example.scala && scala TestWarning! Danger! Warning!Debug! Danger! Debug!I computed a value: 172// INFO lies between WARNING and FINE% scalac -Xelide-below INFO example.scala && scala TestWarning! Danger! Warning!I computed a value: 0Note that only concrete methods can be marked@elidable. A non-annotated method is not elided, even if it overrides / implements a method that has the annotation.
Also note that the static type determines which annotations are considered:
import scala.annotation._, elidable._class C { @elidable(0) def f(): Unit = ??? }object O extends C { override def f(): Unit = println("O.f") }object Test extends App { O.f() // not elided (O: C).f() // elided if compiled with `-Xelide-below 1`}Note for Scala 3 users: If you're using Scala 3, the annotation exists since Scala 3 uses the Scala 2 standard library, but it's unsupported by the Scala 3 compiler. Instead, to achieve the same result you'd want to utilize theinline if feature to introduce behavior that makes a method de facto elided at compile-time.
type LogLevel = Intobject LogLevel: inline val Info = 0 inline val Warn = 1 inline val Debug = 2inline val appLogLevel = LogLevel.Warninline def log(msg: String, inline level: LogLevel): Unit = inline if (level <= appLogLevel) then println(msg)log("Warn log", LogLevel.Warn)log("Debug log", LogLevel. Debug)Attributes
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- elidable.scala
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