* _D_ \- concurrency uses kernel threads or longjmp, with little language support for async semantics * _Nim_ \- has await. Rewrites procedures to be async friendly. Futures that don't rely on kernel threads.
That's basically the biggest factor in my mind for using Nim. Everything I can do in D, I can pretty much do in C, but async futures are not something I can do in C. The strategy in D is to make asynchronicity based on kernel threads, which while fine in theory, doesn't really perform well in IO bound applications, and actually comes with some serious problems since you can't make provable assertions about which thread will run when. Deadlocks, undetectable memory leaks, and all because nobody ever bothered to use D's powerful macro language to implement async/await. They have longjmp based fibers, but they're pretty rudimentary, with no futures, or CPS rewriting or anything. Though longjmp based fibers take a lot of memory, they are relatively fast and deterministic, so await style procedure rewriting isn't strictly necessary. And if you can prove it doesn't _matter_ when each thread is executing, you can make strong assertions about your algorithm, so threaded concurrency _can_ work in theory. So it might be nitpicking to criticize D there. The languages are pretty close in all the other aspects though, and I run into async/await situations a _lot_. So, that 's why I've been using Nim lately. Honestly I _love_ D's syntax to bits. I can't expect a human to be able to understand a language that a code editor cannot logically comprehend enough to auto-indent, so whitespace indented languages like Nim make me a little leery. Also D has those token strings, which aren't precisely hygenic macros, but are pretty easy for a code highlighter to parse. Oh, and Nim's grammar is poorly defined. You'll see terms in the grammar like "typeDescK" which you have to sort of psychically guess the meaning of, since the grammar just never defines it. So D wins in terms of syntax, but... I need my async/await. D's old so it's got a lot of cruft, for what that's worth. (They had to deal with the (ugh) wide character fad.)
