I am in the process of converting some code bases over to using Swift concurrency and am running into a few snags along the way.
The current project I'm working through has a few 3rd party libraries that it relies on, and in one of those libraries, there is a delegate protocol that requires some data values to be returned from its methods.
Here is an example of the type of delegate methods in the library:
public protocol FooDelegate: AnyObject {
func foo() -> CGFloat
}
I'm attempting to return some values from the implementation of the protocol like this:
extension ViewController: FooDelegate {
func foo() -> CGFloat { // <- Cannot satisfy requirement from protocol
view.bounds.height
}
}
Without any modification, the above is implicitly isolated to the MainActor and can not satisfy the requirement from the FooDelegate protocol.
One solution I've tried was to mark the function implementation with nonisolated:
extension ViewController: FooDelegate {
nonisolated func foo() -> CGFloat {
view.bounds.height // <- Cannot be referenced from a non-isolated context
}
}
This did not work though because it references the view controller's view. That results in the view being referenced from a non-isolated synchronous context. (There are also a few other issues with this since any values that are passed through into any of the delegate functions need to conform to Sendable to be able to be passed across actors).
My question is, is there a way to take a 3rd party library and extend it somehow so that it conforms to proper actor isolation without having to modify its source code?
I am checking new Apple documentation on Xcode 13 beta. I am able to build documentation with DocC.
But I am not able to see any documentation created for extensions like String extension, Date extension.
As per example for below case it will not add any documentation.
extension String {
/// Description for DocC
func myMethod() {
}
}
Consider, If I have created an extension for any struct or class, then it is adding documentation like below code
public struct MyStruct {
}
extension MyStruct {
/// Description
func myMethod() {
}
}
Is this default behaviour by apple or I am missing anything?
This is not currently supported. DocC cannot generate documentation for anything but a single module's types. Extensions to types outside your module aren't handled. (It also won't allow you to link to types outside your module using ``...`` references.)
I am starting to learn Swift, and have been following the very good Stanford University video lectures on YouTube. Here is a link if you are interested or it helps (although it isn't required to understand my problem):
Developing iOS 8 Apps with Swift - 2. More Xcode and Swift, MVC
While following the lectures I got to a point where (as far as I could tell) my code was identical to the code in the video but on my system I got a compiler error. After a lot of trial and error I have managed to reduce my code to two examples, one of which generates an error, the other or which doesn't, but I have no idea what is actually causing the error or how to resolve it.
The code which creates the error is:
import UIKit
class BugViewController: UIViewController
{
func perform(operation: (Double) -> Double) {
}
func perform(operation: (Double, Double) -> Double) {
}
}
This creates the following compiler error:
Method 'perform' with Objective-C selector 'perform: ' conflicts with previous declaration with the same Objective-C selector
By simply removing the sub-classing of UIViewController the code compiles:
import UIKit
class BugViewController
{
func perform(operation: (Double) -> Double) {
}
func perform(operation: (Double, Double) -> Double) {
}
}
Some other information which may or may not be relevant:
I have recently upgraded to Yosemite.
When I installed Xcode, I ended up with a Beta version (Version 6.3 (6D543q)) because (if I remember correctly) this was the version I needed to run on my version of OS X.
I am half hoping this is a bug in the compiler because otherwise this doesn't make any sense to me. Any help very gratefully received!
I myself am also taking the Standford course and I got stuck here for a long time too, but after some searching, I found something from here: Xcode release notes and it mentioned something below:
Swift 1.2 is strict about checking type-based overloading of #objc
methods and initializers, something not supported by Objective-C.
// Has the Objective-C selector "performOperation:".
func performOperation(op: NSOperation) { /* do something */ }
// Also has the selector "performOperation:".
func performOperation(fn: () -> Void) {
self.performOperation(NSBlockOperation(block: fn))
}
This code would work when invoked from Swift, but could easily crash
if invoked from Objective-C. To solve this problem, use a type that is
not supported by Objective-C to prevent the Swift compiler from
exposing the member to the Objective-C runtime:
If it makes sense, mark the member as private to disable inference of #objc.
Otherwise, use a dummy parameter with a default value, for
example: _ nonobjc: () = (). (19826275)
Overrides of methods exposed
to Objective-C in private subclasses are not inferred to be #objc,
causing the Swift compiler to crash. Explicitly add the #objc
attribute to any such overriding methods. (19935352)
Symbols from SDKs are not available when using Open Quickly in a
project or workspace that uses Swift. (20349540)
what i did was just adding "private" in front of the override method like this:
private func performOperation(operation: Double -> Double) {
if operandStack.count >= 1 {
displayValue = operation(operandStack.removeLast())
enter()
}
}
Objective-C does not support method overloading, you have to use a different method name. When you inherited UIViewController you inherited NSObject and made the class interopable to Obj-C. Swift on the other hand does support overloading, that's why it works when you remove the inheritance.
As it has already been answered, ObjC doesn't support method overloading (two methods with the same name) and In swift 2 under Xcode 7 there are two options to solve this kind of problems. One option is to rename the method using the attribute: #objc(newNameMethod:)
func methodOne(par1, par2) {...}
#objc(methodTwo:)
func methodOne(par1) {...}
another option to solve this problem in Xcode 7+ is by applying #nonobjc attribute to any method, subscript or initialiser
func methodOne() {...}
#nonobjc
func methodOne() {...}
The problem is UIViewController is an #objc class. When inheriting from UIViewController, BugViewController is also a #objc class.
This means it must conform to the rules of Objective-C selectors (the name of a method). The methods func perform(operation: (Double) -> Double) and func perform(operation: (Double, Double) -> Double) both have the same selector #selector(perform:). This is not allowed.
To resolve this, use different names: like func perform1(operation: (Double) -> Double) and func perform2(operation: (Double, Double) -> Double).
I think the best way to handle this is to give your perform() methods more descriptive names. What do these methods do? How do they change the state of the view controller? Look at the other UIViewController methods to get a feel for the style of method naming, or read Method Names Should Be Expressive and Unique Within a Class
From https://developer.apple.com/library/ios/releasenotes/DeveloperTools/RN-Xcode/Chapters/xc6_release_notes.html under "Xcode 6.3 Release Notes" -> "Swift Language Changes" you find
Swift now detects discrepancies between overloading and overriding in the Swift type system and the effective behavior seen via the Objective-C runtime.
I got the same error due to having having two methods with the same Obj-C signature:
static func prepareForUpSyncing(obj : NSManagedObject!) -> Bool
static func prepareForUpSyncing(objs : [NSManagedObject]!) -> Bool
I didn't want to mark one of them as #nonobjc due to possibility of unforseen consequences at runtime. (Someone can correct me if there is no possibility)
Resolved it by using Swift's external parameter name feature (I made external name same as local name) to the second method, which effectively changes the Obj-c method signature:
static func prepareForUpSyncing(objs objs : [NSManagedObject]!) -> Bool {
I am trying to generate sample data for an #IBDesignable control, so when building for IB I'm fooling the control into being its own datasource. The upshot is I'm adding some methods to a protocol only for use by IB, and as a good citizen I wish to remove these for a regular (non-IB build).
I've distilled my problem down to the following code fragment. My protocol looks like this:-
protocol TestProtocol {
#if TARGET_INTERFACE_BUILDER
func myControl(control:AnyObject, colorForIndex index:UInt) -> UIColor?
func myControl(control:AnyObject, textForIndex index:UInt) -> String?
#endif
}
This fails to compile, with a message that implies an method overloading error: "error: declaration conflicts with previous value". The error message is on the second function declaration, and refers to the first function as the previous declaration it's clashing with.
But these are not overloads, they have different signatures because of the named parameters. And this is such a standard delegate naming convention across Cocoa that I was resistant to renaming my methods without understanding why.
Removing the #if TARGET_INTERFACE_BUILDER fixes the problem, so it is no longer a pressing issue for me, but I am completely stumped as to why adding this conditional compilation would produce such a bizarre error?
I am not sure why it happens, but happen to find a reasonable workaround.
Just separate the two declarations as shown below:
protocol TestProtocol {
#if TARGET_INTERFACE_BUILDER
func myControl(control:AnyObject, colorForIndex index:UInt) -> UIColor?
#endif
#if TARGET_INTERFACE_BUILDER
func myControl(control:AnyObject, textForIndex index:UInt) -> String?
#endif
}
If I have a protocol, MyProtocol defined as:
protocol MyProtocol {
func myFunction() -> String
}
and I have a default implementation declared in an extension so that conformers can "optionally" implement the function:
extension MyProtocol {
func myFunction() -> String { return "" }
}
everything should work just dandy.
However, when a class conforms to that protocol and doesn't implement the functions, the compiler fails with Segmentation fault 11. Once the class implements the function, the error goes away and all is good with the world but it seems to defeat the purpose of defining default implementations in extensions.
Does anyone have any idea why this happens? Is it because the conforming class declares that it implements the methods so the compiler ignores what's written in the extension, can't find the methods and then crashes?
I also had a similar problem with protocol extensions and Segmentation fault 11.
In my case the problem was, that in the extension I put the mutating keyword before the function, but in the protocol there was no mutating. And instead on an error this lead to that Segmentation fault 11.
Maybe that helps a bit.