大量的Scala阶乘有时会崩溃，有时却不会

本文介绍了大量的Scala阶乘有时会崩溃，有时却不会的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

下面的程序经过编译和测试，有时返回结果，有时用填充屏幕

The following program, was compiled and tested, it sometimes return the result, and sometimes fills the screen with

java.lang.StackOverflowError at scala.BigInt$.apply(BigInt.scala:47) at scala.BigInt.equals(BigInt.scala:129) at scala.runtime.BoxesRunTime.equals(Unknown Source) at bigint$.factorial(fact2.scala:3) at bigint$.factorial(fact2.scala:3) ...

程序:

object bigint extends Application { def factorial(n: BigInt): BigInt = if (n == 0) 1 else n * factorial(n-1) println("4391! = "+factorial(4391)) }

我的问题:

• 是因为JVM上发生堆栈溢出，有时会发生，有时却不会吗?
• 这种不确定性行为是否被视为错误?
• 我认为Scala不会将其尾巴递归吗?我怎样才能做到这一点?

详细信息:

Scala编译器版本2.7.5.final- LAMP/EPFL Scala版权所有2002-2009 代码运行程序版本2.7.5.final- 版权所有2002-2009，LAMP/EPFL

Scala compiler version 2.7.5.final -- Copyright 2002-2009, LAMP/EPFL Scala code runner version 2.7.5.final -- Copyright 2002-2009, LAMP/EPFL

java版本"1.6.0_0" OpenJDK 运行时环境(构建 1.6.0_0-b11)OpenJDK客户端VM(内部版本1.6.0_0-b11，混合模式，共享)

java version "1.6.0_0" OpenJDK Runtime Environment (build 1.6.0_0-b11) OpenJDK Client VM (build 1.6.0_0-b11, mixed mode, sharing)

Ubuntu 2.6.24-24-通用

Ubuntu 2.6.24-24-generic

推荐答案

如果递归调用是函数中的最后一条语句，则尾调用优化将仅在Scala中起作用.这是非常有限的. Scala书中说:

Tail-call optimization will only work in Scala if the recursive call is the last statement in the function. It's very limited. The Scala book says:

[...]尾调用优化为 限于以下情况 方法或嵌套函数调用自身 直接作为最后的操作 无需通过函数值 或其他中介.

[...] tail-call optimization is limited to situations in which a method or nested function calls itself directly as its last operation, without going through a function value or some other intermediary.

在您的情况下，递归调用是较大表达式的一部分，它本身并不是最后一个操作-这里的最后一个操作是乘法.

In your case, the recursive call is part of a larger expression, and is not itself the very last operation - the last operation here is the multiplication.

本文演示了如何制作它可以工作:

This article demonstrates how to make it work:

class Factorial { def factorial(n: Int): Int = { def factorialAcc(acc: Int, n: Int): Int = { if (n <= 1) acc else factorialAcc(n * acc, n - 1) } factorialAcc(1, n) } }