I don't know Rust, but code looks readable. Function apply receives two arguments and returns function of one argument (address of b) which returns value of typ

I don't know Rust, but code looks readable. Function apply receives two arguments and returns function of one argument (address of b) which returns value of type C. I assume function apply() creates closure, so a.clone() is necessary to create fresh copy of a every time when closure is called. b is passed by reference, so code is generic. Not bad.