> - Swift’s generics are dynamic by default, which involves wrapping up every object into a possibly-heap-allocated container and using dynamic dispatch for eve

> - Swift’s generics are dynamic by default, which involves wrapping up every object into a possibly-heap-allocated container and using dynamic dispatch for everything. You're right about the dynamic dispatch, but both specialized and unspecialized generics use the same memory layout. While unspecialized generics have to compute the layout dynamically if needed, there's no boxing required. If this were not the case, specialized and unspecialized code would not be able to interoperate (and as you said, this is a requirement because of ABI boundaries). > - No stack-allocated arrays in Swift; all collections are reference-counted and stored on the heap. There's a compiler optimization pass which stack-allocates reference counted objects with a known lifetime (which includes the backing storage for arrays). However, just as with generic specialization, this is a best-effort optimization and is not guaranteed to actually take place.