from: swift-users mailing list Basically, @escaping is valid only on closures in function parameter position. The noescape-by-default rule only applies to these closures at function parameter position, otherwise they are escaping. Aggregates, such as enums with associated values (e.g. Optional), tuples, structs, etc., if they have closures, follow the default rules for closures that are … Read more
Use a Stream: Stream.of(find1(), find2(), find3()) .filter(Optional::isPresent) .map(Optional::get) .findFirst(); If you need to evaluate the find methods lazily, use supplier functions: Stream.of(this::find1, this::find2, this::find3) .map(Supplier::get) .filter(Optional::isPresent) .map(Optional::get) .findFirst();
Not setting a read-only (constant) field with either an: initialization expression initializer is almost certainly an indication of an error in your program. Since you have no other opportunity to set the value of your let field, the value of the field is going to remain nil (or some other default). It is rather unlikely … Read more
This is part of JDK 9 in the form of or, which takes a Supplier<Optional<T>>. Your example would then be: return serviceA(args) .or(() -> serviceB(args)) .or(() -> serviceC(args)); For details see the Javadoc or this post I wrote.
This answer is in response to the question in the title, “Shouldn’t Optional be Serializable?” The short answer is that the Java Lambda (JSR-335) expert group considered and rejected it. That note, and this one and this one indicate that the primary design goal for Optional is to be used as the return value of … Read more
If you are using Java 9+, you can use ifPresentOrElse() method: opt.ifPresentOrElse( value -> System.out.println(“Found: ” + value), () -> System.out.println(“Not found”) );
In a type declaration the ! is similar to the ?. Both are an optional, but the ! is an “implicitly unwrapped” optional, meaning that you do not have to unwrap it to access the value (but it can still be nil). This is basically the behavior we already had in objective-c. A value can … Read more
Take these two scenarios: Optional<Foo> opt = … Foo x = opt.orElse( new Foo() ); Foo y = opt.orElseGet( Foo::new ); If opt doesn’t contain a value, the two are indeed equivalent. But if opt does contain a value, how many Foo objects will be created? P.s.: of course in this example the difference probably … Read more
if let and guard let serve similar, but distinct purposes. The “else” case of guard must exit the current scope. Generally that means it must call return or abort the program. guard is used to provide early return without requiring nesting of the rest of the function. if let nests its scope, and does not … Read more
It is almost always unnecessary to check if an optional is not nil. Pretty much the only time you need to do this is if its nil-ness is the only thing you want to know about – you don’t care what’s in the value, just that it’s not nil. Under most other circumstances, there is … Read more