I’ve always wondered why units(1) isn’t a library. I’d love to have access to abstract “united quantities” and “united measurements” in my HLL of choice, rather than needing to switch to a special-purpose tool (units, Frink) or a statistical-analysis language like R just to get them.

Sometimes I need to bust out stoichiometry-like unit-balancing in the middle of my code, and I want type enforcement that I’m getting the right units in the output! Sometimes I want to do a series of floating-point calculations, and I need to put error-bars on the result, and it’d be great if those were tracked for me in the form of a measurement ADT that tracked sig-figs. Etc.

My only guess for why there’s no libunits, is that it’d be a obtrusive black-box of operational non-guarantees if it was implemented in C, given that what Units does — if naively implemented — would be heavy on arbitrary memory allocations, and basically necessitate garbage collection.

It’d make much more sense for a libunits to exist as a C++-ish “template library” that takes an allocator as an argument; but that doesn’t really help anyone who wants to use any language other than C++ (as the template parameters can’t be exposed in the C wrapper code that other languages FFI to.)

(Before someone asks, you could get a limited kind of united-quantities — ones that can only represent “realistic” units — with a static per-qty bitfield representing the compiled-in units. But this wouldn’t really let you represent arbitrary unexpected “unit polynomial” qtys, e.g. m^5s^-3. This might seem fine, but sometimes intermediate quantities in formulae look like that, even though they work out to something sensible when everything is multiplied out.)

Even if there couldn’t be a single units library implementation, it’d at least make sense for there to be 1. a canonical libunits-data release (sort of like tzdata), that individual library impls could pull in; and 2. a high-level API spec or reference-impl of what a libunits library for a given language-runtime would look like (sort of like how every HLL has copied JodaTime’s datetime design.)