What I want in a language of this class is some ability to transition code from a slow/dynamic/generalized/exploratory phase to fast/static/specialized/checked.

What I want in a language of this class is some ability to transition code from a slow/dynamic/generalized/exploratory phase to fast/static/specialized/checked. Both D and Nim offer features of that nature. (Something like Rust omits itself by forcing memory into a central role, leading to a lot of annotation boilerplate - it's correct for writing Servo or similarly complex parallelized systems, but I am not writing Servo.) When I left Nim, it was because I had serious concerns about the project being able to tame its rapid accumulation of features. I had no faith in all the things it advertised to actually work correctly. The dev process I witnessed was "cave in to toxic people who whinged a lot." D has a lot of warts from being around longer, but in the end, what I want to write code in anger with is something that can boast a well-engineered compiler, and D has not one compiler but more than one. That was years ago. To win me back you'll have to market a demonstration of similar stability. Zig is in a different category from any other option because its design allows me to tackle a piece of low-hanging fruit: a modernization of old C libraries that does not reinvent the universe, create a new ABI, introduce a runtime, or otherwise disrupt the original context. I can write basically the same kind of code in the same kind of style, but the language automatically pushes my attention to more edge cases and undefined conditions, and the compiler simplifies the build process, removing the preprocessor noise that tends to appear in substantial libraries.