> On Nov 16, 2018, at 2:25 PM, Alexander Yakushev <unlo...@bytopia.org> wrote:
>
> Could you please give a brief rationale for why metadata-polymorphism is now
> opt-in? I'm wondering what kind of the undesired behavior this is meant to
> prevent.
Doing the metadata check affects the performance of invocations of external
protocol extensions (does not affect perf of direct definitions).
As one of the goals of protocols is to be fast, we decided to make this an
explicit opt-in choice (for now at least). In cases where metadata protocol
extension is useful, the protocol creator can choose to add that at the cost of
a small perf hit.
Significant time was spent analyzing the performance issues and looking at
other options, but in the end this seemed like the best compromise for now.
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