I’ll first say that this is my opinion, and that I don’t have good suggestions for how Julia as a language should implement this, just that it should:

* Better language level support for testing

* Better language level support for docstrings
- currently doc strings are just normal strings stored in a global struct, and are missing crucial information about the type signature of structs or functions or methods that are being documented

* A way to type hint without using multiple dispatch / interfaces
- I want to be able to say this argument has fields x, y, z but I don’t want to use multiple dispatch to enforce this interface. Multiple dispatch is useful with the implementation details of your code depend on the data structure. But I want better static type checking for a handful of fields or methods. Typescript is absolutely awesome at this.

* Support for using @copied s.x = 1 where s is an immutable struct. Users are literally incentivized to use mutable structs instead of immutable structs because that results in shorter cleaner syntax, even though performance drops through the roof in that case. With immutable structs you’ll have to recreate the struct by calling the constructor. In most cases, the compiler will compile as this away anyway but users are going to prefer shorter cleaner syntax when writing code.

* Better macro support. Currently macros have to be valid Julia code, meaning you end up with weird dsl that only kind of sort of matches the domain being modeled. In rust and nim I can literally copy almost any syntax and paste it in a macro block and it’ll just work. This is more work for macro developers and probably will make inference harder but will improve readability.

* Language level support for extending Array or letting users define arrays that are as efficient as the built in ones.

* Similar request for String buffers.

* Rewrite parser that is currently in scheme in Julia, I suspect better tooling will fall out of this

* Support for a subset of Julia that is fast to compile and run and produces small binaries.

I think more generally I want Julia to be a slightly different language than it is ( or possibly ever can be ). Currently a user of Julia needs to be cognizant of too many things that could accidentally introduce type instability. Almost none of these problems are going to be encountered by someone that understands how compilers work / how computers work, which in my experience is not a lot of domain scientists but is a lot of the core team working on Julia. Domain scientists have PhDs or Masters in highly niche subjects after years of writing Python, R, or Matlab but are more often than not terrible software engineers. I can’t tell how many times in almost a decade of being in this field have I seen 10,000 line scripts in a single file without any comments written by extremely smart scientists. Guiding these folk from the get go to make better software engineering decisions is important imo. Currently, if I’m leading a project, I can’t trust a fresh graduate or junior engineer to write idiomatic type stable fast and extensible Julia code, even if they are the experts of their domain. They have to be experts of their domain AND awesome software engineers which is so rare to find. Given additional constraints about funding, writing proposals, documentation etc, it’s honestly kind of amazing that Julia’s libraries are as good as they are.

In my opinion, Julia really shines when one or two people have to write code to tackle a specific problem. Code is super concise and clean and it all fits in your head and everything is fine and dandy. But when you have an engineering team that needs to work with databases, authentication, logging, deployment, scaling, machine learning, data analysis and plotting, and do most if not all of that in Julia … it’s so easy to write something that gets checked in that passes tests and code review that just destroys performance benchmarks.