Comment by lll-o-lll
Yuck. I thought some of the signatures you end up with when building “Modern C++” in the Andrei Alexandrescu style were hairy, but this looks sick. Not in a good way.
Probably does something cool for all that crazy though?
Yuck. I thought some of the signatures you end up with when building “Modern C++” in the Andrei Alexandrescu style were hairy, but this looks sick. Not in a good way.
Probably does something cool for all that crazy though?
Every requirement on the types is commented on why it's necessary.
This is a generic method in the middle of some database DSL code that does a bunch of SQL operations on a type safe manner. Code like this takes "SELECT ?+* FROM ?+* WHERE ? ORDER BY ?+* LIMIT ? OFFSET ?", specifically the limit and offset part, and returns a type that will always map to the database column. If the query is selecting a count of how many Foo each Baz references, this will map to a paginated Foo to Baz count type.
The alternative is to manually write this stuff out in SQL, then manually cast the right types into the basic primitives, which is what a language like Zig probably does.
You'll find similar (though sometimes less type-safe) complex code in just about any ORM/DSL, whether it's written in Java or PHP.
I don't think you can accomplish this in C without some kind of recursive macro parser generating either structs or maybe function pointers on the fly. It'd be hell to make that stuff not leak or double free memory, though.