> but I think one's ability to be productive in a language is highly correlated with how much of the language (and project domain) they can "keep in their head"

> but I think one's ability to be productive in a language is highly correlated with how much of the language (and project domain) they can "keep in their head" at a time. I disagree. I'd say productivity has very little to do with language familiarity and way more to do with ecosystem familiarity. C++ is hard because the ecosystem has no real entry point and several "script language to write a script language to write a compilation definition to write a script language to compile a project" build systems. (Who's familiar with M4?)