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You can use a virtual function to downcast like this:

I think it is a bug in Funding Choices.

Deep down in some ad-blocking detection code loaded by Funding Choices I found the following being part of a reportClientEvent(...) call:

You can start with pow(ALPHABSIZE, DIGITS - 1) and use integer division to get each place value/table index. On each loop you successively reduce by a factor of ALPHABSIZE down to 1. This lets you output left to right.

Logarithms are not necessary to compute here. To compute an integer logarithm you could nevertheless just count the number of passes through a while/for loop in the same fashion.

You simply iterate over the values of the dictionary, check whether the value of the 'key' item is in your list and if that's the case, append the value of the 'name' item to your output list.

Let jsonObj be your JSON object presented in your question. Then this code should work:

and an extension function which converts the API into a hot flow

This extension looks correct, however the flow is not hot (nor should it be). It only registers a callback when an actual collection starts, and unregisters when the collector is cancelled (this includes when the collector uses terminal operators that limit the number of items, such as .first() or .take(n)).

This is quite an important note to keep in mind for your other questions.

In the absence of that SupervisorJob(), it appears that test will never end. Maybe collecting the flow never ends for some reason, which I don't understand

As mentioned above, due to how the flow is constructed (and how the CallbackApi works), the flow collection cannot end by decision of the producer (the callback API). It can only stop by cancellation of the collector, which will also unregister the correponding callback (which is good).

The reason your custom job allows the test to end is probably because you're escaping structured concurrency by overriding the job in the context by a custom one that doesn't have that current job as parent. However you're likely still leaking that neverending coroutine from the scope that is never cancelled.

I'm feeding captured callback in a separate coroutine.

And that's correct, although I don't understand why you call removeListener from this separate coroutine. What callback are you unregistering here? Note that this also cannot have any effect on the flow, because even if you could unregister the callback that was created in the callbackFlow builder, it wouldn't magically close the channel of the callbackFlow, so the flow wouldn't end anyway (which I'm assuming is what you tried to do here).

Also, unregistering the callback from outside would prevent you from checking it was actually unregistered by your production code.

2- If I remove the launch body which callbackSlot.captured.onResult(10) is inside it, test will fail with this error UninitializedPropertyAccessException: lateinit property captured has not been initialized. I would think that yield should start the flow.

yield() is quite brittle. If you use it, you must be very conscious about how the code of each concurrent coroutine is currently written. The reason it's brittle is that it will only yield the thread to other coroutines until the next suspension point. You can't predict which coroutine will be executed when yielding, neither can you predict which one the thread will resume after reaching the suspension point. If there are a couple suspensions, all bets are off. If there are other running coroutines, all bets are off too.

A better approach is to use kotlinx-coroutines-test which provides utilities like advanceUntilIdle which makes sure other coroutines are all done or waiting on a suspension point.

Now how to fix this test? I can't test anything right now, but I would probably approach it this way:

• use runTest from kotlinx-coroutines-test instead of runBlocking to control better when other coroutines run (and wait for instance for the flow collection to do something)
• start the flow collection in a coroutine (just launch/launchIn(this) without custom scope) and keep a handle to the launched Job (return value of launch/launchIn)
• call the captured callback with a value, advanceUntilIdle() to ensure the flow collector's coroutine can handle it, and then assert that the list got the element (note: since everything is single threaded and the callback is not suspending, this would deadlock if there was no buffer, but callbackFlow uses a default buffer so it should be fine)
• optional: repeat the above several times with different values and confirm they are collected by the flow
• cancel the collection job, advanceUntilIdle(), and then test that the callback was unregistered (I'm not a Mockk expert, but there should be something to check that removeListener was called)

Note: maybe I'm old school but if your CallbackApi is an interface (it's a class in your example, but I'm not sure to which extent it reflects the reality), I'd rather implement a mock manually using a channel to simulate events and assert expectations. I find it easier to reason about and to debug. Here is an example of what I mean

AFAIK, function expressions are treated as any other variables by JavaScript engines

They aren't.

A function expression evaluates to a value which is a function. Unlike a function declaration they do not create a variable as a side effect.

Try this:

memset(p, 0, n) sets to all-bits-0.
An initializer of { 0 } sets to the value 0.
On just about any machine you've ever heard of, the two concepts are equivalent.

However, there have been machines where the floating-point value 0.0 was not represented by a bit pattern of all-bits-0. And there have been machines where a null pointer was not represented by a bit pattern of all-bits-0, either. On those machines, an initializer of { 0 } would always get you the zero initialization you wanted, while memset might not.

See also question 7.31 and question 5.17 in the C FAQ list.

Postscript: It's not clear to me why mbstate_t would be a "classic example" of this issue, though.

P.P.S. One other difference, as pointed out by @ryker: memset will set any "holes" in a padded structure to 0, while setting that structure to { 0 } might not.