The recommend way to check elapsed time/performance is using the measure function that is available in XCTests.

It isn't reliable to write your own measure blocks, since the performance (and therefore execution/elapsed time) of a block of code is influenced by e.g. CPU caches.

The second time a function is invoked, would likely be quicker than the first time it is invoked, although it can vary a few %. Therefore 'benchmarking' by using your own closures (given all over the place here) can give different results than your code being executed in production by real users.

The measure function invokes your block of code several times, mimicking the performance/elapsed time of your code like it is used in production (at least gives more accurate results).

The recommend way to check elapsed time/performance is using the measure function that is available in XCTests.

It isn't reliable to write your own measure blocks, since the performance (and therefore execution/elapsed time) of a block of code is influenced by e.g. CPU caches.

The second time a function is invoked, would likely be quicker than the first time it is invoked, although it can vary a few %. Therefore 'benchmarking' by using your own closures (given all over the place here) by executing it once, can give different results than your code being executed in production by real users.

The measure function invokes your block of code several times, mimicking the performance/elapsed time of your code like it is used in production (at least gives more accurate results).