Martin R, yes this is directly related to "Fastest way to get (const) pointer to struct for inter-operability with C/C++”, in the sense I discovered it while working on that issue. The sample code I wrote is doing a copy simply because in the non-mutating case, it cannot pass a pointer to the its internal data, and in the case when the internal data is a var, as we already observed, the withUnsafePointer optimization doesn’t kick in (not that it does anyway with let either right now)...