为什么要创建“Implicitly Unwrapped Optionals"，因为这意味着您知道存在价值? [英] Why create "Implicitly Unwrapped Optionals", since that implies you know there's a value?

问题描述

Why would you create a "Implicitly Unwrapped Optional" vs creating just a regular variable or constant? If you know that it can be successfully unwrapped then why create an optional in the first place? For example, why is this:

let someString: String! = "this is the string"

going to be more useful than:

let someString: String = "this is the string"

If "optionals indicate that a constant or variable is allowed to have 'no value'", but "sometimes it is clear from a program’s structure that an optional will always have a value after that value is first set", what is the point of making it an optional in the first place? If you know an optional is always going to have a value, doesn't that make it not optional?

解决方案

Consider the case of an object that may have nil properties while it's being constructed and configured, but is immutable and non-nil afterwards (NSImage is often treated this way, though in its case it's still useful to mutate sometimes). Implicitly unwrapped optionals would clean up its code a good deal, with relatively low loss of safety (as long as the one guarantee held, it would be safe).

(Edit) To be clear though: regular optionals are nearly always preferable.

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