Accelerate is a pure C API. Metal is an Objective-C API. It is possible to call arbitrary Objective-C APIs from pure C using the Objective-C runtime functions

Accelerate is a pure C API. Metal is an Objective-C API. It is possible to call arbitrary Objective-C APIs from pure C using the Objective-C runtime functions, and Apple themselves recently released a Metal API wrapper written in C++ that works this way. [1] I wouldn't recommend that approach, though. With Objective-C being an almost-pure superset of C, it's a lot easier to just build your code in Objective-C mode and make native Objective-C calls where necessary. [1] https://news.ycombinator.com/item?id=29289761 https://news.ycombinator.com/item?id=29289761