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I needed something like this today, but I didn't want to add a full scale extension for just the one place and wanted something more functional (more thread safe?). I also didn't need to protect against negative indices, just those that might be past the end of an array:
I know Swift is a memory safe language and I also know that Rust is a memory safe language so my question is what language in general is safer? Are they on par or is one better than another? I'm a Swift and Rust developer and by the complexity of Rust I've just assumed Rust is safer but I never really knew for sure.
Some of the complexity of Rust makes it possible to prove the absence of data races (under certain global assumptions). For example, Rust's type system can prevent you from sharing an unprotected reference to mutable memory across threads. This complexity does make Rust safer than Swift in the presence of concurrency; Swift has to rely on the programmer to avoid data races, at least for now.
Some of the other complexity of Rust makes it possible to safely express certain interesting things in local scopes. For example, in Rust you can build an array of references to the elements of another array, and you can then pass that around freely as long as it doesn't escape the lifetime of the original array. You can see this as adding safety, since if you wanted to express exactly that in Swift you would need to use unsafe abstractions and thus lose some memory-safety. Alternatively, you can see it as a complexity/performance trade-off, since there are probably ways to achieve the programmer's original high-level goal that don't require an array of references into another array (perhaps less efficient ways), and the ability to express this undoubtedly adds complexity to the language.
Neither of them have traditional garbage collection. Rust has compile-time garbage collection, and Swift has ARC, and Rust's garbage collection does a much better job than ARC, so I would go with Rust, just avoid using unsafe blocks.
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I got dictionary.subscript.getter in my crash logs. Basically I have not respected the fact that in Swift, dictionaries are not thread safe. For a quick dirty fix I have thought about putting all the interactions on the main queue which should hopefully eliminate the issues. That can be done for writes but is a bit more complicated for reads as I can't return from an async call (or at least not in a way that would be feasible).
In "Identifying objects in Swift" we took a look at how objects can be identified using the built-in ObjectIdentifier type - and this week, we're going to construct similar identifier types for values, with an increasing degree of type safety.
As a language, Swift puts a heavy focus on types and type safety. With features like generics, protocols and static typing, we're always encouraged (or forced even) to know the exact types of the objects and values that we're dealing with.
While strings are nice for things like text, they're not a very robust or safe solution for something like identifiers. Not every string is a valid identifier, and ideally we'd like to leverage the type system to prevent bugs that can occur when accidentally passing an incompatible string as an identifier.
First up, let's make it possible to create an identifier using a string literal. That way, we get the same convenience as when using plain strings, but with the added safety of using a dedicated type. To do that, all we have to do is conform to ExpressibleByStringLiteral and implement an additional initializer:
So even though having a dedicated Identifier type is a huge step towards better type safety, we can still take things further by associating a given identifier with the type of value that it's representing. To do that, let's add a generic Value type to Identifier:
Having type-safe identifiers is not only useful when it comes to preventing developer mistakes, it also enables us to construct some really nice APIs when it comes to handling our models and values in different contexts. For example, now that we have the Identifiable protocol, we could make our database code type-safe as well:
Using type-safe identifiers can be a great way to make our model code more robust and less prone to errors caused by accidentally using the wrong kind of identifier. It also enables us to leverage the compiler in interesting ways throughout our code base, in order to make handling models and values a lot simpler and more safe.
What degree of type safety that will be appropriate for your code will of course vary a lot depending on your exact setup and requirements. Simply using a dedicated, non-generic Identifier type might be enough, and can both be easy to implement and be a big step towards more type-safe identifier handling. If you want or need even more type safety, using generics and protocols can also be a great option when taking things further.
What do you think? What kind of identifiers do you use, and what kind of type safety do you like your identifiers to have? Let me know - along with any questions, comments or feedback you might have - on Twitter @johnsundell.
NASA's Neil Gehrels Swift Observatory operations team has confirmed that a failed reaction wheel caused the spacecraft to enter safe mode Jan. 18. The team believes the issue is mechanical and is moving to configure the spacecraft to operate using the other five reaction wheels, which are performing as expected.
On the evening of Tuesday, Jan. 18, NASA's Neil Gehrels Swift Observatory entered into safe mode, suspending pointed science observations. The mission team is investigating a possible failure of one of the spacecraft's reaction wheels as the cause.
The team has powered off the suspected wheel. The observatory and all its instruments are otherwise healthy and operating as anticipated. The observatory will remain in safe mode as a precaution while the team further investigates the issue.
We define an instance method, safelyAccessElement(at:), that accepts the index of the element we would like to access. Notice that the return type of the instance method is Element?. Element is the type of element the array stores. The return type is of an optional type because the instance method returns nil if the value of index is out of bounds.
The safelyAccessElement(at:) instance method solves the problem we set out to solve, but there is an even better solution. We can define a subscript to safely access an element by its index. We need to make a few changes to the previous implementation. First, we remove the func keyword. Second, we replcae the name of the instance method with the subscript keyword. Third, we change the argument label from at to safe to make the intent of the subscript more obvious.
I define this subscript in every project I work on to avoid index out of range exceptions. The syntax looks nice and, thanks to the name of the argument label, there is no confusion or conflict with the default or unsafe subscript.
Given this, there are a few important things to note. The concept of atomicity is distinct from the concept of thread-safety. Atomicity does not imply thread-safety, but if something is thread-safe it must be atomic.
However, in the case of global constants (let) or static let members on structs, enums, and classes in Swift, we can say that they are thread-safe, because they are atomic and immutable.
Swift guarantees atomicity and a synchronized initialization for all globals and static members, but only those declared as let are thread-safe after initialization because they are immutable. (And we know that immutable values are safe to access across threads.) For global var declarations or static var members, we cannot claim that they are thread-safe because they could be mutated across threads after initialization.
The safe area of a view reflects the area not covered by navigation bars, tab bars, toolbars, and other ancestors that obscure a view controller's view. (In tvOS, the safe area reflects the area not covered by the screen's bezel.) You obtain the safe area for a view by applying the insets in this property to the view's bounds rectangle. If the view is not currently installed in a view hierarchy, or is not yet visible onscreen, the edge insets in this property are 0.
For the view controller's root view, the insets account for the status bar, other visible bars, and any additional insets that you specified using the additionalSafeAreaInsets property of your view controller. For other views in the view hierarchy, the insets reflect only the portion of the view that is covered. For example, if a view is entirely within the safe area of its superview, the edge insets in this property are 0.
The following guide walks you through how to gather the safe area insets and apply them to your screens. This process uses TinyConstraints, a library that facilitates NSLayoutConstraints and builds on our existing Open Source Swift starter project.
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