scala - 按名称参数与匿名函数

Question

仍然不清楚的是，在延迟评估和其他好处(如果有的话)方面，与匿名函数相比，名称参数的优势是什么:

def func1(a: => Int)
def func2(a: () => Int)

我应该什么时候使用第一个，什么时候使用第二个？

这不是 What's the difference between => , ()=>, and Unit=> 的副本

Answer 1

懒惰在这两种情况下是相同的，但有细微的差别。考虑:

def generateInt(): Int = { ... }
def byFunc(a: () => Int) { ... }
def byName(a: => Int) { ... }

// you can pass method without
// generating additional anonymous function
byFunc(generateInt)

// but both of the below are the same
// i.e. additional anonymous function is generated
byName(generateInt)
byName(() => generateInt())

但是，按名称调用的函数对于制作 DSL 很有用。例如:

def measured(block: ⇒ Unit): Long = {
  val startTime = System.currentTimeMillis()
  block
  System.currentTimeMillis() - startTime
}

Long timeTaken = measured {
  // any code here you like to measure
  // written just as there were no "measured" around
}