隐式展开时的可选绑定可选

问题描述

Swift编程指南说:您还可以使用带有可选绑定的隐式解包后的可选内容，以在单个语句中检查和解开它的值".当值已经解包时，为什么需要使用可选绑定?选项绑定会再次将其解包吗?

Swift Programming Guide says "You can also use an implicitly unwrapped optional with optional binding, to check and unwrap its value in a single statement". Why do you need to use optional binding when the value is already unwrapped? Does option binding unwrap it again?

推荐答案

调用隐式解包与使用！调用常规可选对象相同！之后.它仍然可以保留nil值，当它为nil时调用它会导致运行时错误，因此，如果不确定是否为nil，可以使用if let可选绑定.

Calling an implicitly unwrapped is the same as calling a regular optional with ! after it. It can still hold a nil value and calling it when it's nil will result in a runtime error, so you use the if let optional binding if you aren't sure if it is nil or not.

var myOptional: Int! = nil

10 + myOptional //runtime error

if let myUnwrapped = myOptional{
    10 + myOptional //safe
}

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