weak-references - w3toppers.com

Do capture lists of inner closures need to redeclare `self` as `weak` or `unowned`?

The [weak self] in anotherFunctionWithTrailingClosure is not needed. You can empirically test this: class Experiment { func someFunctionWithTrailingClosure(closure: @escaping () -> Void) { print(“starting”, #function) DispatchQueue.main.asyncAfter(deadline: .now() + 1) { closure() print(“finishing”, #function) } } func anotherFunctionWithTrailingClosure(closure: @escaping () -> Void) { print(“starting”, #function) DispatchQueue.main.asyncAfter(deadline: .now() + 1) { closure() print(“finishing”, #function) } } func … Read more

What is the difference between a weak and a block reference?

From the docs about __block __block variables live in storage that is shared between the lexical scope of the variable and all blocks and block copies declared or created within the variable’s lexical scope. Thus, the storage will survive the destruction of the stack frame if any copies of the blocks declared within the frame … Read more

How to delete every reference of an object in Python?

No no no. Python has a garbage collector that has very strong territory issues – it won’t mess with you creating objects, you don’t mess with it deleting objects. Simply put, it can’t be done, and for a good reason. If, for instance, your need comes from cases of, say, caching algorithms that keep references, … Read more

using python WeakSet to enable a callback functionality

You cannot create weak references to method objects. Method objects are short lived; they are created on the fly as you access the name on the instance. See the descriptor howto how that works. When you access a method name, a new method object is created for you, and when you then add that method … Read more

Garbage Collection should have removed object but WeakReference.IsAlive still returning true

Hit the same issue as you – my test was passing everywhere, except for under NCrunch (could be any other instrumentation in your case). Hm. Debugging with SOS revealed additional roots held on a call stack of a test method. My guess is that they were a result of code instrumentation that disabled any compiler … Read more

Does WeakReference make a good cache?

Using WeakReferences as the primary means of referencing cached objects is not really a great idea, because as Josh said, your at the mercy of any future behavioral changes to WeakReference and the GC. However, if your cache needs any kind of resurrection capability, use of WeakReferences for items that are pending purge is useful. … Read more

Using block and weak

__block is a storage qualifier. It specifies that the variable should directly be captured by the block as opposed to copying it. This is useful in case you need to modify the original variable, as in the following example __block NSString *aString = @”Hey!”; void(^aBlock)() = ^{ aString = @”Hello!” }; // without __block you … Read more

Weak reference benefits

Soft and phantom references come from Java, I believe. A long weak reference (pass true to C#’s WeakReference constructor) might be considered similar to Java’s PhantomReference. If there is an analog to SoftReference in C#, I don’t know what it is. Weak references do not extend the lifespan of an object, thus allowing it to … Read more

Is Josh Smith’s implementation of the RelayCommand flawed?

I’ve found the answer in Josh’s comment on his “Understanding Routed Commands” article: […] you have to use the WeakEvent pattern in your CanExecuteChanged event. This is because visual elements will hook that event, and since the command object might never be garbage collected until the app shuts down, there is a very real potential … Read more

Using weak self in dispatch_async function

Assuming, self is an object pointer to a UIViewController. Things to consider: A UIViewController is a “UIKit” object. UIKit objects shall not be sent methods on non-main threads, that is – those methods must execute on the main thread only! A block that has been enqueued in a queue – whether this was synchronously or … Read more