* Support for using @copied s.x = 1 where s is an immutable struct.
I believe the standard package for this is this:
https://github.com/jw3126/Setfield.jl#usage
* Currently macros have to be valid Julia code,
There are two kinds of macros, and it sounds like you want `macro foo_str(x)` which accepts anything. But the tradeoff is that you have to parse it, rather than getting an expression tree.
https://docs.julialang.org/en/v1/manual/metaprogramming/#met...