我想用评论详细说明之前的答案并对解决方案进行评估:
import scala.reflect.runtime.universe.{Quasiquote, runtimeMirror}
import scala.tools.reflect.ToolBox
object Runtime {
def time[R](block: => R): R = {
val t0 = System.nanoTime()
val result = block // call-by-name
val t1 = System.nanoTime()
println("Elapsed time: " + (t1 - t0) + " ns")
result
}
def main(args: Array[String]): Unit = {
val mirror = runtimeMirror(getClass.getClassLoader)
val tb = ToolBox(mirror).mkToolBox()
val data = Array(1, 2, 3)
println(s"Data before function applied on it: '${data.toList}")
val function = "def apply(x: Int): Int = x + 2"
println(s"Function: '$function'")
println("#######################")
// Function with tb.eval
println(".... with tb.eval")
val functionWrapper = "object FunctionWrapper { " + function + "}"
// This takes around 1sec!
val functionSymbol = time { tb.define(tb.parse(functionWrapper).asInstanceOf[tb.u.ImplDef])}
// This takes around 0.5 sec!
val result = time {data.map(x => tb.eval(q"$functionSymbol.apply($x)"))}
println(s"Data after function applied on it: '${result.toList}'")
println(".... without tb.eval")
val func = time {tb.eval(q"$functionSymbol.apply _").asInstanceOf[Int => Int]}
// This takes around 0.5 sec!
val result2 = time {data.map(func)}
println(s"Data after function applied on it: '${result2.toList}'")
}
}
如果我们执行上面的代码,我们会看到以下输出:
Data before function applied on it: 'List(1, 2, 3)
Function: 'def apply(x: Int): Int = x + 2'
#######################
.... with tb.eval
Elapsed time: 716542980 ns
Elapsed time: 661386581 ns
Data after function applied on it: 'List(3, 4, 5)'
.... without tb.eval
Elapsed time: 394119232 ns
Elapsed time: 85713 ns
Data after function applied on it: 'List(3, 4, 5)'
只是为了强调进行评估以提取函数然后应用于数据的重要性,而不是再次评估,正如答案中的评论所表明的那样。