The article mentions one: const folding. I don't think we need a benchmark to suggest that could mean a performance improvement in some cases. Regardless, to

The article mentions one: const folding. I don't think we need a benchmark to suggest that could mean a performance improvement in some cases. Regardless, to me this isn't about performance, this is about "integrity" (to use the same term as in the JEP): consumers of my library should not be mucking about in private implementation details, and then inevitably complaining about problems to me when something breaks. If you need a feature that I don't expose, ask for it (or better yet, submit a patch). Sure, I've used reflection to modify library internals before, but I recognize that whenever I do that I'm inviting a maintenance headache into my world. But some people just think things should always work, even when they are breaking them.