More efficient and movable Defer - #11005
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The refactor makes `Defer` without `std::function` and thus without all the overhead (like allocation and type erasure) that comes with it. I've also enabled the move constructor and assignment operators, whose lack is what got me started on this refactor in the first place. There are only two call-sites that needed to be adapted, one in ApiListener, because the `SetFunc()` method has been removed. And one in/around `ConfigPackageUtility` because that needs the type declared in the header which gets (slightly) more complicated now.
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This refactor makes
Deferwork withoutstd::functionby default and thus without all the overhead (like allocation and type erasure) that comes with it. It also makesDefer-objects movable.std::function<void()>is still supported by explicit instantiation along withvoid(*)()pointers when a fixed function type is needed with and without capture.Other Changes
There are only two call-sites that needed to be adapted,
ApiListener::ReplayLog()gets an explicitly instantiatedDefer<std::function<void()>>so the code can keep usingDefer::SetFunc(). And the use aroundConfigPackageUtilitygets an explicitDefer<void(*)()>because the type needs to be available in the header and thus can't be deduced.Reasoning
Aside from the obvious efficiency gains the reason I started on this refactor was because I wanted to move a
Deferobject into a lambda-capture and noticed that it had the move constructor disabled. I then looked into what possible reason there could be for the disabled move constructor and didn't find any, but then noticed that by templatingDeferand adding a deduction guide to astd::optional<lambda>,std::functioncould be avoided entirely. So this is a little more than the bare minimum I needed, but still it's a nice improvement, I think.Additional Options
The changes in
ConfigPackageUtilitycurrently minimize the diff, but theShared<Defer>::Ptrthere could easily be avoided as well. This would however mean slight changes in the potential lifetime of the defer which should be evaluated carefully. I can do that in this PR if anyone wants me to.