A PHP internals mailing list discussion about a proposed RFC for bound-erased generic types in PHP. The RFC proposes adding generic type parameters to classes, interfaces, traits, functions, methods, closures, and arrow functions with bounds, defaults, and variance markers. Type parameters erase to their bound at runtime, with the pre-erasure form preserved for Reflection and static analyzers. The discussion covers key design decisions including: type parameter ordering restrictions, intersection type constraints, arity validation (opt-in via turbofish syntax), diamond inheritance checks, the turbofish `::< >` syntax choice, and `+`/`-` variance markers. The RFC author responds point-by-point to feedback, clarifying that arity validation is opt-in at call sites using turbofish, explaining why diamond inheritance is rejected at link time, and defending the turbofish syntax over context-sensitive alternatives.
