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Valentin Shergin
059142935a
Summary: Quite often in the Fabric codebase, we need to iterate on a list of shadow nodes and perform some work depending on the exact type (or kind) of shadow node we have. Today, we exclusively use RTTI to test for exact type. The problem here is that RTTI is not only expensive in terms of code size (we are moving towards removing RTTI), it's expensive in terms of CPU cycles. (Don't mistake RTTI/dynamic_cast overhead with dynamic dispatch overhead!) `dynamic_cast` has it's own advantages, of cource: it's simple and straight-forward and does not require additional configuration. On the other side, it requires knowledge about exact class relationship configuration and knowing the exact name of the class. ShadowNodeTraits is the generalized solution for storing predefined traits right inside ShadowNode object and check/set/unset them efficiently and in a particular-class-independent manner. This diff only implements it in general and switching storing an internal flag of ShadowNode inside the trait collection to save some space (and for illustration purposes as well). In the coming diff, we will see how this approach allows tackling the real, non-trivial problem. In addition to the concept, this diff implements some convenience infra, such as `ConcreteShadowNode::BaseTraits()` static method that allows designating intrinsic-to-a-class traits declaratively. Changelog: [Internal] Fabric-specific internal change. Reviewed By: sammy-SC Differential Revision: D18525348 fbshipit-source-id: 083bb85e0a9dc9d6c69bf395bd338d3c18def688