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This has been my experience as well. It can be extraordinarily difficult to design a consistent OO type system to represent things like quantities with units an

by stult 6y ago

This has been my experience as well. It can be extraordinarily difficult to design a consistent OO type system to represent things like quantities with units and references, alongside quantities with just units and neither units nor references. For example, altitude is a quantity plus a unit of distance plus a reference (eg above ground level). Except some references require different data to convert. So AGL requires elevation for conversion to mean sea level, for example. Designing an OO system to represent that and constrain against invalid operations gets super complex and the developer ergonomics rapidly degrade in most languages. I’ve only ever successfully done it in C#, and even then I’ve found maintaining the unit conversion code annoying.

Smaug123 6y ago
Have you tried F#, which has units of measure (with no runtime cost, due to erasure) built in?
TeMPOraL 6y ago
Using your example, in the limit you end up with a data type carrying a chain of conversions with it, that reference some database that you don't own, but have to maintain access to. That altitude's reference itself is a particular geographical coordinate system (of many possible GCSes) that references a particular datum ("on what planet are we, and how does it look", of many possible datums), both of which are maintained by third-party organizations and political in nature. And then when you have another altitude with a slightly different reference, you have to handle conversions between them. At which point you may decide you just want to represent altitude with reference = "same as everywhere else in the program, because if it's the same, it doesn't matter what it is". Which is what most non-GIS code does, except it isn't documented explicitly, and it's up to the user or integrator to ensure the data fed to the program uses the same reference as the user expects to see.

by stult 6y ago

Smaug123 6y ago

Have you tried F#, which has units of measure (with no runtime cost, due to erasure) built in?

TeMPOraL 6y ago

Using your example, in the limit you end up with a data type carrying a chain of conversions with it, that reference some database that you don't own, but have to maintain access to. That altitude's reference itself is a particular geographical coordinate system (of many possible GCSes) that references a particular datum ("on what planet are we, and how does it look", of many possible datums), both of which are maintained by third-party organizations and political in nature. And then when you have another altitude with a slightly different reference, you have to handle conversions between them. At which point you may decide you just want to represent altitude with reference = "same as everywhere else in the program, because if it's the same, it doesn't matter what it is". Which is what most non-GIS code does, except it isn't documented explicitly, and it's up to the user or integrator to ensure the data fed to the program uses the same reference as the user expects to see.