Swift 可选参数未解包 [英] Swift optional parameter not unwrapped

问题描述

我有一个带有可选参数(位置)的函数.我测试它为零，但 Xcode 仍然向我显示一个错误:可选类型 Int 的值?未解包"并建议我使用！"或?".

I have a function with a optional parameter(position). I test for it to be nil but still Xcode shows me an error: "Value of optional type Int? not unwrapped" and suggests me to use "!" or "?".

var entries = [String]()

func addEntry(text: String, position: Int?) {
    if(position == nil) {
        entries.append(text)
    } else {
        entries[position] = text
    }
}

我是 Swift 的新手，不明白为什么这不行.在这个 if 子句中，编译器应该 100% 确定该位置已定义，或者?

Im new to Swift and don't understand why this isn't ok. Within this if-clause the compiler should be 100% sure that position is defined, or?

推荐答案

有几种方法可以正确编码:

There are a few ways to code this properly:

func addEntry(text: String, position: Int?) {
    // Safely unwrap the value
    if let position = position {
        entries[position] = text
    } else {
        entries.append(text)
    }
}

或:

func addEntry(text: String, position: Int?) {
    if position == nil {
        entries.append(text)
    } else {
        // Force unwrap since you know it isn't nil
        entries[position!] = text
    }
}

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