Sonic is a super fast auto suggestion engine built by the team at crisp.chat, a customer engagement platform. its built in Rust and they officially support a javascript client, but if you want to use sonic via php, this is the library that you can look for. Completely unit tested, and adheres to modern coding standards, and offers a clean api to interact with sonic.
A collection consists of buckets which can be termed as objects too. But basically what FLUSHC does is emptying out the collection. So Both are same. But I am merging your suggestion. Thanks for your contribution.
I am a very newbie and know nothing about sonic but I guess it is a mistake.