Generators

This section contains language-specific generators and guidance for using the artifacts they produce. Choose a target below to explore the details.

Feature support matrix

Every generator implements the full IDL surface (structs, enums, interfaces, optionals, lists, maps, typed handles, borrowed parameters, builders, typed error domains with opt-in throws, and nested modules) plus the call shapes below. A generator that cannot support a feature declares it in its TargetCapabilities, and weaveffi generate fails loudly when an IDL uses a feature the selected target cannot deliver (no silent skips).

Notes:

• Iterators are lazy. Every target wraps the C ABI’s handle/_next/_destroy triple in its native lazy idiom (Go iter.Seq, Swift Sequence, C++ input-iterator range, Kotlin Iterator, JS iterables, Python iterators, .NET IEnumerable<T>, Dart Iterable, Ruby Enumerator), pulling one element per consumer step and destroying the handle exactly once. C exposes the raw symbols directly.
• Go and Ruby async wrappers block the calling thread until the producer’s completion callback fires (a channel receive in Go, a Queue#pop in Ruby). Run them from a goroutine or Ruby thread for concurrency; the native producer still runs off-thread.
• Wasm callbacks/listeners deliver synchronously. The loader installs one long-lived JavaScript trampoline per callback typedef in the module’s function table, so the producer’s emit_* dispatches straight back into JS. Because wasm32-unknown-unknown is single-threaded, events fire only while a call into the module is on the stack; a producer that emits from a spawned thread cannot run on this target at all (details). In Emscripten mode callbacks, listeners, and async functions become explicit throwing stubs rather than silent no-ops.