[Webkit-unassigned] [Bug 189272] New: [WTF] Add support for compactly storing multiple optional members in a class

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=189272

            Bug ID: 189272
           Summary: [WTF] Add support for compactly storing multiple
                    optional members in a class
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Web Template Framework
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: sam at webkit.org

Created attachment 348845

  --> https://bugs.webkit.org/attachment.cgi?id=348845&action=review

Proof of concept

When you have a class that has multiple std::optional members (and you aren't using CompactOptional from https://bugs.webkit.org/show_bug.cgi?id=189231) you end up wasting a lot of space due to the bool each std::optional must contain. I think we can do better.

An initial idea, attached as a proof of concept, is to store the bools all together as a bitset and have each optional member be able to access that bitset via some OBJECT_OFFSETOF fun. This requires a bit of macro nastiness and bit more typing per optional value, so I am not 100% sure it's worth it.

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