<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Jan 12, 2016, at 7:46 PM, Luke Howard via swift-dev <<a href="mailto:swift-dev@swift.org" class="">swift-dev@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Would it be possible to extend GenericParameterDescriptor to include a tail-emplaced set of references to ProtocolDescriptors for any parameter type constraints that require witness tables? This would be useful plumbing for a future API that can dynamically instantiate generic types.</div><div class=""><br class=""></div><div class="">See:</div><div class=""><br class=""></div><div class=""><a href="https://github.com/lhoward/swift/blob/SR-381/include/swift/Runtime/Metadata.h#L1199" class="">https://github.com/lhoward/swift/blob/SR-381/include/swift/Runtime/Metadata.h#L1199</a></div><div class=""><br class=""></div><div class=""><a href="https://github.com/lhoward/swift/blob/SR-381/stdlib/public/runtime/MetadataLookup.cpp#L338" class="">https://github.com/lhoward/swift/blob/SR-381/stdlib/public/runtime/MetadataLookup.cpp#L338</a></div></div></div></blockquote><br class=""></div><div>That's something to consider. However, we will be systematically revamping these metadata structures soon, so I don't think there's much benefit to incrementally changing what we have.</div><div><br class=""></div><div>-Joe</div><br class=""></body></html>