dreampiggy / zconform

A constant time replacement for the O(n) as? in Swift

ZConform

A replacement for as? which runs in constant time instead of O(n) when the conformance is not satisfied.

How it works

ZConform does a one-time scan of all conformances when intialized with ZConformHelper.setup(). This populates a cache that can quickly verify if there are no conformances for a type/protocol pair. See the blog post for more details.

When to use it

If you have many as? casts for different type/protocols and have many (thousands) of conformances in your app, the runtime's default conformance check doesn't work well. It will do a linear scan of all conformances each time a new type/protocol combination is checked. If you know not all the casts will be successful ZConform likely speeds up your app since it can avoid the O(n) operation entirely.

Limitations

This implementation is not production ready. It builds the cache as new images are loaded with _dyld_register_func_for_add_image but doesn't have any safeguards if this cache update is performed while a conformance check is ongoing on a different thread. It's also not supporting class bound protocols, and only supports checking conformance of structs. Objective-C bridging also would require a separate implementation, it only works with types defined purely in Swift.

If you‘re interested in productionizing this in your app, please get in touch