> On Aug 11, 2016, at 7:16 AM, Sebastian Hagedorn via swift-users
> <swift-users@swift.org> wrote:
>
> We often write code that returns early, but has to make sure a bit of code
> (e.g., a completion handler) is always called whenever we return, which seems
> like a great use case for defer. I started to write this:
>
> func execute(with completion: ((Bool) -> Void)?) {
> var success = false
> defer {
> // should always execute with the current state of success at
> that time
> completion?(success)
> }
>
> guard … else {
> // completion is expected to be executed with false
> return
> }
>
> success = true
>
> // completion is expected to be executed with true
> }
>
> However, it seems that defer copies the state of success, which means any
> update to the variable is not respected, and the completion block is always
> called with false.
>
> Is there a way to make this work? I could image to call a function within the
> defer block that evaluates the success (e.g., depending on the state of an
> instance variable), but using a local variable seems to encapsulate this a
> lot better.
This is a bug. Defer should track updates of the variable. Would you mind
filing this at bugs.swift.org? Do you happen to know whether it reproduces only
in debug or release builds, or both?
-Joe
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