> It seems like further advances in this space either require giving the compiler a better understanding of what is "actually" shared In the context of arrays,

> It seems like further advances in this space either require giving the compiler a better understanding of what is "actually" shared In the context of arrays, it helps when programmers use higher-order combinators/functions, e.g. maps. There is a mutable way to do a map, and an immutable way, and which should be used in the compiled program depends on analysis of where the variable is used.