def getStr(): String = {
println("getStr is running")
"str"
}
def lazyHello(para: => String) = {
println("lazy hello is runing")
println(para)
}
def notLazyHello(para: String) = {
println("not lazy hello is runing")
println(para)
}
def anoyHello(para: () => String) = {
println("anoy hello is runing")
println(para())
}
notLazyHello(getStr)
lazyHello(getStr)
anoyHello(getStr)
得到这个结果:
scala> notLazyHello(getStr)
getStr is running
not lazy hello is runing
str
scala> lazyHello(getStr)
lazy hello is runing
getStr is running
str
scala> anoyHello(getStr)
anoy hello is runing
getStr is running
str
似乎lazyHello 和anoyHello 执行相同。
那么,在 Scala 中,什么时候是使用惰性求值参数而不是使用函数作为参数的好时机呢?