swift-corelibs-libdispatch | libdispatch Project , ( a.k.a | Architecture library

Note the .cpp extension. This is C++ code.

1. The operator ... = delete syntax says that this operator should be suppressed, generating a compiler warning if you try to use it.

2. The inline qualifier is a performance optimization. To quote from The C++ Programming Language:

   The inline specifier is a hint to the compiler that it should attempt to generate code for a call of [the function] inline rather than laying down the code for the function once and then calling through the usual function call mechanism.

   If (a) a function is small; and (b) performance is of paramount concern, you can use inline qualifier so that the compiler will, effectively, just insert the code of the function wherever you use it rather than saving it as a function and calling it you normally would. This saves the modest overhead of calling the function.

If you need help understanding C++, I’d suggest you check out these resources.

A dispatch_data_t is an sequence of bytes. The bytes can be stored in multiple non-contiguous byte arrays. For example, bytes 0-6 can be stored in an array, and then bytes 7-12 are stored in a separate array somewhere else in memory.

For efficiency, the dispatch_data_apply function lets you iterate over those arrays in-place (without copying out the data). On each call to your “applier”, you receive a pointer to one of the underlying storage arrays in the buffer argument. The size argument tells you how many bytes are in this particular array, and the offset argument tells you how (logically) far the first byte of this particular array is from the first byte of the entire dispatch_data_t.

Example: