斯威夫特使方法参数可变吗? [英] Swift make method parameter mutable?

问题描述

如何在不创建其他变量的情况下处理此错误?

How can I deal with this error without creating additional variable?

func reduceToZero(x:Int) -> Int {
    while (x != 0) {
        x = x-1            // ERROR: cannot assign to 'let' value 'x'
    }
    return x
}

我不想创建其他变量只是为了存储x的值.甚至有可能做我想做的事吗?

I don't want to create additional variable just to store the value of x. Is it even possible to do what I want?

推荐答案

如其他答案所述，从Swift 3开始，将var放在不推荐使用的变量之前.尽管没有在其他答案中说明，但是可以声明inout参数.想一想:传入一个指针.

As stated in other answers, as of Swift 3 placing var before a variable has been deprecated. Though not stated in other answers is the ability to declare an inout parameter. Think: passing in a pointer.

func reduceToZero(_ x: inout Int) {
    while (x != 0) {
        x = x-1     
    }
}

var a = 3
reduceToZero(&a)
print(a) // will print '0'

这在递归中特别有用.

Apple的inout声明准则可以在

Apple's inout declaration guidelines can be found here.

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