pub type Callback<U, R> = unsafe extern "C" fn(cif: &ffi_cif, result: &mut R, args: *const *const c_void, userdata: &U);Expand description
The type of function called by a closure.
U is the type of the user data captured by the closure and passed
to the callback, and R is the type of the result. The parameters
are not typed, since they are passed as a C array of void*.