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> In my opinion, checking whether a variable is null or not is easier than using ? and ! everywhere. Which is why you can do exactly that. if let checked
by stormbrew 11y ago
> In my opinion, checking whether a variable is null or not is easier than using ? and ! everywhere.
Which is why you can do exactly that.
if let checked = blah { /* checked does not need ! or ? */ }
- tpritc 11y agoYou still need to use ! inside that block, but you can use it confidently that it won't result in you accidentally unwrapping a null object.
- stormbrew 11y agoNo, you use checked instead of blah. If blah is type 'Blah?', Checked is type 'Blah'. Edit to add: And unless something has changed since I last tried it, you can also just shadow blah so that inside that scope you're referring to the unwrapped one: if let blah = blah { /* use blah here, it's unwrapped */ } It looks kind of silly, but I have used it where there was no better name for the unwrapped value.
- billconan 11y agothis doesn't look better than c++ syntax. I still don't understand the point of ! and ? less is more, swift ought to know.
- stormbrew 11y agoI don't think it's trying to be syntactically better than C++. It's an improvement in semantics. Once you unwrap an optional with "if let", it cannot cause an access violation. You seem to be insisting on using ! and then blaming the language for letting you shoot your foot off with it...
- billconan 11y agoSorry, I don't get it. the example you gave is like the following c++ code: XXX *object = null; if ((object = anotherpointer) != NULL) { ... } The point is, ! is only useful, when it can detect null pointers during compiling time. but it doesn't. the way ! is used, as suggested by your example, is also doable in C++, it is just a habit thing. in c++, with good habit, you won't have problem. in Swift with bad habit, you will have the same problem. then what good is !,
- stormbrew 11y agoNo, you don't seem to be getting what I'm saying. I'm saying don't use !, and showing you how to avoid using it in a common pattern. Using 'if let' instead of ! does give you compile time verification of correctness. ! is there for the small number of cases where that's not possible. And it makes it much more obvious where you've got a potential problem, because the '!' is a literal code smell. You can't really do that with c++.
- yoz-y 11y agoEver since the guard statement was introduced I think you should never, ever use the ! as operator. It still has some sense when using as a type, for example for IBOutlets.
- billconan 11y agoI'm curious, if my variable "a" is indeed null, and when I say a!, what will happen? will it be a runtime error? like a memory access violation in c++? what's the benefit of adding !? if it generates the same access violation runtime error?
- rockshassa 11y agoyes, it is a runtime error. given the code let foo = bar! If bar is nil, you'll get a runtime error "unexpectedly found nil when unwrapping bar" in my opinion, the benefit of optionals in general is that it allows you to guarantee at compile time that certain variables (non optionals) will _never_ be nil, which enables all kinds of compiler optimizations.
- sulam 11y agoArguably the newly supported guard syntax is nicer: guard let foo = optFoo { Swift.print("oops, this optional thing wasn't optional") } Swift.print("now \(foo) is in scope and non-nil")