Comment by zbentley
2 days ago
Specifically, that the lack of tagged unions (or really, structured return types in general; you can pretend those are a tagged union if you believe hard enough) in C library interop conventions is a terrible foundation on which to build widely-used APIs.
And that just ends up indicting the C language itself. Can't send errors down a separate channel; folks might not inspect errno. Can't return NULL on error, folks might compare it blindly to another result. No tagged unions, so can't return one. Can't crash on error because there's no scoped error handling. Can't return a struct for checking .error/.result separately, because alignment and equality (and tearing and accidental clobbering and more) make that brittle as hell for widely-used APIs.
C is not a good language for library APIs. Like, really not. It has its uses/strengths, sure, but without even getting into the typical gripes people have about C, libraries--one of the things that it is used for the most--are one of the things for which it is the least well-suited.
"But it has a stable ABI!" So does a land mine.
you can return a struct just fine... most API's don't though.
Historically it didn't work well between different compilers. Maybe it still doesn't.
Passing and returning structs by value has been part of C since C89. Most compilers pass small structs in individual registers, and nowadays with LTO they'll even elide the copy of bigger ones if they can. What's definitely the case though is that by-value structs weren't a common thing when most of the Unix API was written.
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