What's the difference between this and company-clang?

[ohmree]

I'm using Spacemacs and have tried both it's c-c++ layer which uses company-clang and this private layer which uses irony and so far I could see two differences:

• Spacemacs' layer supports .clang_complete but I assume it's not that hard to add support for that in the irony layer, so this is a win for Spacemacs' default layer (not really for company-clang though)
• Spacemacs' layer also didn't use C++14 by default so it didn't recognize constexpr. There may be an option to change that but with Irony I got that to work out of the box

So are there any other differences between the two? Which one is better when it comes to performance and features?

[Sarcasm]

I can't really answer much about these "Spacemacs layers" as I'm not really familiar with Spacemacs.

But to answer the title of your question, company-irony is supposed to be faster than company-clang. Because irony-server runs as a subprocess of Emacs and can keep informations between edits of a file, instead of launching a compiler instance every time the completion is requested (which is what company-clang does). Feature-wise, the compilation database stuff is supposed to be an improvement over specifying the compile options manually for each file.