Pointers in swift: purpose of UnsafeMutableBufferPointer

Question

Currently looking into swift pointers.

UnsafePointer and UnsafeMutablePointer provide a pointer to a byte. By using pointer arithmetic, you can access the rest of the bytes.

Something similar can be done with a UnsafeMutableBufferPointer, which has an endIndex parameter. So what is the advantage/difference of using UnsafeMutableBufferPointer over UnsafeMutablePointer when accessing for example the bytes in NSData?

Answer 1

UnsafeMutablePointer<T> is designed for accessing a single element of type T. Its interface is designed for accessing a single scalar value.

UnsafeMutableBufferPointer<T>, on the other hand, is designed to access a group of elements of type T stored in a contiguous block of memory. Its interface is designed to access individual elements of the range, and also for treating the entire collection as a single unit (e.g. the generate method).

If you access bytes inside NSData, UnsafePointer alone is not sufficient, because you need to know the length of data. In contrast, a single UnsafeBufferPointer is sufficient to represent the data, because it provides both the initial location and the number of elements.