This is my biggest gripe with golang; I want to be able to write functional extensions for the blessed generic types (slice, map etc.), but can't. Until we can do things like this, or implement our own generic types, golang will be a niche language.
I don't think so. What you're saying is you want to apply a niche concept (fp, I know it's getting traction, but still pretty niche in the business world) to an OO language and have a hard time doing that. Golang is niche right now too, but the lack of functional ability is probably not going to to hugely affect anything.
I'd disagree that FP is niche; the concepts are used throughout business, and more and more back ends are being written in an FP language. Front ends using JS are being written more and more in an FP style as well.
