What was it about headers?

In terms of rebuild performance in defining the interface vs implementation, there is interest in having rustc handle that automatically, see https://rust-lang.github.io/rust-project-goals/2025h2/relink...

That change sounds like a big improvement if they manage to do it!

Changing the private module fragment (equivalent of a source file) shouldn't cause rebuilds since it doesn't change the interface.

D modules are very fast. Many of our customers rely on D being way faster than C++ to compile.

I often hear about a lot of advantages of D. So I don't understand why it is so unpopular. Probably I need to give it a chance, but I'm unsure that I will find a real job with the D stack.

Most languages that have made it big have been the primary language for a platform that made it big, and it is really the features of the platform more than those of the language that have driven that.

> Most languages that have made it big have been the primary language for a platform that made it big,

I think you're going to want to define "made it big" and then make yourself some lists as this to me sounds like it doesn't have much explanatory power.

D is fine. Like many languages that postdate C++ and Java, it made better choices, learning from the past. But it doesn't really have a differentiator.

Knowing D will make you a better programmer in other languages. For example, D pushes you to write better encapsulated modules, which is a transferable skill.

How does D avoid the problem I described?

For one thing, it never has to compile a module more than once, no matter how many times it is imported. For another, the compilation of a module is done on demand. For a third, D modules can be "header only", omitting the implementation.