【Scala十四】Scala核心八：闭包
编程技术 / houtizong 发布于 3年前 72
Free variable A free variable of an expression is a variable that’s used inside the expression but not defined inside the expression. For instance, in the function literal expression (x: Int) => (x, y), both variables x
and y are used, but only y is a free variable, because it is not defined inside the expression.
Bound variable A bound variable of an expression is a variable that’s both used and defined inside the expression. For instance, in the function literal expression (x: Int) => (x, y), both variables x and y are used,
but only x is bound, because it is defined in the expression as an Int and the sole argument to the function described by the expression.
closure A function object that captures free variables, and is said to be “closed” over the variables visible at the time it is created.
闭包是一个函数对象，当闭包中的自由变量绑定了具体的值后，称之为闭包
问题：
对于闭包(x: Int) => (x, y)，当闭包建立后，y的值发生改变，调用闭包时，y的值是建立时的值还是改变的值？答案是改变后的值。也就是说，闭包函数是在调用执行时才从当前的上下文中获取到y的值
package spark.examples.scala.closureobject ClosureTest { def sum(args: List[Int]) = { var sum = 0 //sum += _是函数常量，其中sum是自由变量 val calc = sum += (_: Int) args.foreach(calc) println("sum1: " + sum) //6， sum是自由变量，计算结束后，sum的值在闭包内的变化，能够在外面也看到 args.foreach(calc) //sum的值改变后，函数常量能够看到这个变化，再次计算结果12 println("sum2: " + sum) //12, } def increaseBy(offset: Int) = { def add(x: Int) = { x + offset } add _ //方法体可以直接使用 (x: Int) => x + offset } def main(args: Array[String]) { val args = List(1, 2, 3) sum(args) println(increaseBy(10)(100)) //110 }}
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