D is a real anomaly to me because it should have had the same trajectory as Rust, it vastly improved upon other systems languages at conception, the authors evangelized it, including at FAANG, and yet, Rust seems to have gained traction everywhere D failed to do so. Even in places where C++ has historically been shunned, Rust has some traction (Linux Kernel). I now believe that language adoption is just a product of the right news cycles and timing, and perhaps hype over the creators or a certain feature. I am sad we got Rust and not D. D is so much easier to grok as a C++ person, and I think Rust is incredibly verbose looking.
I don't find it particularly surprising. D uses a garbage collector while C, C++ and Rust do not. D's GC can be disabled but that isn't that useful when most D code including the standard library until just a few years ago were not written with that in mind.
D is much more closely a competitor of C# than it is C++. D has a few nice features like advanced compile time programming but the actual nuts and bolts that Staff engineering management looks isn't really solid. D's GC is a design straight out of the 80's. Dmd has good compiler throughout but code quality isn't very good. Ldc is much better but compile times are much longer.
Adopting languages at FAANG beyond a single team just yolo deploying them to production requires integrating dozens of engineering systems for everything from post mortem debugging to live profiling to authentication systems. The cost to do this is in the order of tens of millions of dollars.
D just isn't suitable as a C or C++ replacement in the places that actually require it and the cost to enable it in large companies isn't worth it for the incremental improvement it does offer in some areas.
Rust has memory safety without GC, and a from-scratch language design. D is an evolutionary development of C++ (which is also gaining new features of its own) with little to recommend it besides. A comparison with Carbon and cppfront is also instructive, note that both of those have not added GC to the language.
Culture matters. "Culture eats strategy for breakfast". Rust has a safety culture. Yes it has a bunch of safety technology but the technology doesn't decide how things are used. It would be legal using the Rust compiler to implement the IndexMut trait on slices such that it just YOLOs like a C++ index. Rust doesn't do that, not because somehow the technology forbids it - it does not - but because culturally it's anathema to them.
When I heard about D it was often in combination with issues that seemed rather basic. Like multiple mutually exclusive runtime libraries that made D libraries incompatible with each other from the start, or hard version breaks that where trying to solve fundamental issues but also caused projects to lag behind for years. Have you seen how long the Python 2 to 3 migration took? The news cycles didn't do anything to fix that mess either.
