Taking TTFX seriously: Can we make common packages faster to load and use

General Usage Performance
15

Exploring the linked issues, led me to a (seemingly esoteric) thing that is being done with kwargs to help with type inference.

Instead of function f(...; kw::Bool=false) people seem to be doing function f(...;kw::Val{T}=Val(false)) where T.

I think I am seeing things like this in these OrdinaryDiffEq and Polyester changes:

https://github.com/SciML/OrdinaryDiffEq.jl/pull/1473/files#diff-8ce813ea8d7f370bc91b5ac1526a80f7fd354be769bafdd6b12b7368f3ae90a9L395

https://github.com/JuliaSIMD/Polyester.jl/commit/5e6ae4c2ae009b507bbcf90ff2c2b9b7d5e94559#diff-a523f7f63af3c48f517501d7e392926093393f7d033fb208f477568ec30bec38L72

Why is this necessary? Why is it better than saying the keyword will be of type Bool?

EDIT: discourse seems to be stripping out the anchors from the links above making it difficult to tell which lines I am talking about. Here are the SciML and Polyester links with anchors.