org.specs2.control.LazyParameter.scala Maven / Gradle / Ivy
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package org.specs2
package control
import Exceptions._
/**
* This trait can be used to allow some function to be called with varargs, with values being
* evaluated lazily:
* {{{
* def method[T](values: LazyParameter[T]*) = {
* values.toStream // use the toStream method to consume the values lazily
* }
* // usage
* method(exp1, exp2, exp3)
* }}}
*
* Note that the values are really evaluated once, unlike a by-name parameter.
*/
trait LazyParameters {
/** transform a value to a zero-arg function returning that value */
implicit def lazyParameter[T](value: =>T): LazyParameter[T] = new LazyParameter(() => value)
}
object LazyParameters extends LazyParameters
/** class holding a value to be evaluated lazily */
class LazyParameter[+T](private val v: () => T) {
private lazy val evaluated = v.apply()
/**
* @return the evaluated value. This method is private to specs2 to avoid the implicit to leak to client
* specifications, if the user has defined a 'value' method somewhere in his code
*/
private[specs2] def value = evaluated
override def toString = tryOrElse(value.toString)("Evaluation error")
override def equals(o: Any) = value == o
override def hashCode = value.hashCode
def map[S >: T](f: T => S) = LazyParameters.lazyParameter(f(value))
}