确定Swift字典是否包含键并获取其任何值 [英] Determining if Swift dictionary contains key and obtaining any of its values

问题描述

我目前正在使用以下（笨拙）代码来确定（非空）Swift字典是否包含给定的键，并从同一个字典中获取一个（任何）值。

I am currently using the following (clumsy) pieces of code for determining if a (non-empty) Swift dictionary contains a given key and for obtaining one (any) value from the same dictionary.

如何在Swift中更加优雅？

How can one put this more elegantly in Swift?

// excerpt from method that determines if dict contains key
if let _ = dict[key] {
    return true
}
else {
    return false
}

// excerpt from method that obtains first value from dict
for (_, value) in dict {
    return value
}

推荐答案

您不需要任何特殊代码来执行此操作，因为它是什么字典已经有。当您获取 dict [key] 您知道字典是否包含密钥，因为您可以返回的可选项不是 nil （它包含的值）。

You don't need any special code to do this, because it is what a dictionary already does. When you fetch dict[key] you know whether the dictionary contains the key, because the Optional that you get back is not nil (and it contains the value).

所以，如果你只是想回答问题字典包含密钥，请问：

So, if you just want to answer the question whether the dictionary contains the key, ask:

let keyExists = dict[key] != nil

如果你想要的值，而你知道，字典包含密钥，说：

If you want the value and you know the dictionary contains the key, say:

let val = dict[key]!

但是，如果通常发生，您不知道它包含密钥 - 您要获取它使用它，但只有存在 - 然后使用类似如果让：

But if, as usually happens, you don't know it contains the key - you want to fetch it and use it, but only if it exists - then use something like if let:

if let val = dict[key] {
    // now val is not nil and the Optional has been unwrapped, so use it
}

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