One simple but non obvious (at least to me) trick when implementing tagged unions: put the union discriminator/tag at the end, not the beginning - that way a pointer to a union is also a pointer to the value, no need to increment the pointer to point past the tag after discriminating.
What is the best source for cross-language description of language features? Eg: “optional types”: which langs have them and how do they work? Same with “union types” etc.
There's no single oracle for these things, unfortunately. One common citation is "Types and Programming Languages" by Benjamin Pierce (2002), but otherwise people generally just use the nomenclature of a specific language and hope cross-linguistic adventurers will figure it out. I think there's somewhat less variance with more modern languages, though, so in some ways it's less of an issue than it once was.
(2025) And about CopperLang (203 points, 3 days ago, 120 comments) https://news.ycombinator.com/item?id=50308754
Swift has already answered all these questions.
One simple but non obvious (at least to me) trick when implementing tagged unions: put the union discriminator/tag at the end, not the beginning - that way a pointer to a union is also a pointer to the value, no need to increment the pointer to point past the tag after discriminating.
when serializing these things it's generally going to be best to put the tag first though. That way it's cheap to figure out how to parse it.
What is the best source for cross-language description of language features? Eg: “optional types”: which langs have them and how do they work? Same with “union types” etc.
There's no single oracle for these things, unfortunately. One common citation is "Types and Programming Languages" by Benjamin Pierce (2002), but otherwise people generally just use the nomenclature of a specific language and hope cross-linguistic adventurers will figure it out. I think there's somewhat less variance with more modern languages, though, so in some ways it's less of an issue than it once was.
Rosetta code is often helpful. Not exactly for language features, necessarily: https://rosettacode.org/wiki/Monads/Maybe_monad
i read Onion Types
Philomena Cunk on Programming
https://www.youtube.com/shorts/XK_D7Z-cKZ4
Well poor design can require you to peel off multiple layers of optionals, and so they're often a significant smell just like onions are.
Shrek would argue the layers are a feature not a bug
No matter how you cut them, they'll make you cry.
So shallot be...