The C++ code is a simple list type, and also a bunch of tests for that type to confirm that it works as intended. The crucial trick here is that because static asserts are used, the test values are computed during compilation, such computations are forbidden (by the standard) from having any leaks or Undefined Behaviour. Anything allocated must be freed by the time the tests complete, and no language Undefined Behaviour is permitted.

The latter is pretty normal for other languages but is a big deal in C++ where UB is a constant plague. However many languages have either forbid or have strict limits on compile time heap allocation - after all that heap isn't going to still exist at runtime. Requiring that you free everything allocated fixes that hole and means you get free leak detection.