You're not answering my question. I have a bunch of numeric code where I have dense matrices, sparse matrices, diagonal matrices, etc.

I have heterogenous priority queues where I want to push in JSON data and plain strings, I have custom iterators, concurrent data structures, default dictionaries, etc.

Seriously, look up Python's itertools and data structure modules and realize that there's a wealth of things that are useful and practical and, above all, reduce code size while preserving interface contracts and semantics. Go is completely unsatisfactory in this regard.