Andreas Rossberg wrote:
Actually, I don't see why this should have a measurable impact on performance in practice. The "generic" case is dog-slow for JavaScript anyway, what matters is how easy it is to specialise for the types actually seen at runtime. And there, this would just add yet another row to the (already complex) matrix of cases for receiver/index type pairs that you optimize for. The same might actually be true for symbols, depending on the implementation strategy.
Probably I'm more sensitive to the "generic" case, which while dog slow still dogs some real-world critical paths (if not fake/lame/old benchmarks).
It all costs, David is proposing yet another cost. Maybe that's my final answer :-|.
Like any new type or representation, it may cause deoptimization and increased polymorphism, but that's nothing new under the sun, and we are adding plenty of that with ES6.
In contrast, private symbols (any symbols, public/unique or private) should benefit from existing property-in-receiver optimizations. Right?
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