ABAP 中的断言

Question

Over the years I've written code in a variety of languages and environments, but one constant seemed to be the consensus on the use of assertions. As I understand it, they are there for the development process when you want to identify "impossible" errors and other situations to which your first reaction would be "that can't be right" and which cannot be handled gracefully, leaving the system in a state where it has no choice but to terminate. Assertions are easy to understand and quick to code but due to their fail-fast nature are unsuitable for development code. Ideally, assertions are used to discover all development bugs and then removed or turned off when shipping the code. Input or program states that are wrong, but possible (and expected to occur) should instead be handled gracefully via exceptions or other error handling techniques.

However, none of this seems to hold true for writing ABAP code for SAP. I've just spent the better part of an hour trying to track down the precise location where an assert was giving me an unintelligible error. This turned out to be five levels down in standard SAP code, which is apparently riddled with ASSERT statements. I now know that a certain variable identifying a table IS NOT INITIAL while its accompanying variable identifying a field is.

This tells me nothing. The Web Dynpro component running this code actually "catches" this assert, showing me a generic error message, which only serves to prevent the debugger from launching when the assert is tripped.

My question therefore is what the guidelines or best practices are for the use of assertions in ABAP. Is this SAP writing bad code? Is it an accepted practice to fill your custom code with asserts and leave them in when shipping the code? If so, how would we go about handling these asserts in runtime so that the application doesn't crash and burn while still being able to identify the cause of the error?

Answer 1

The guidelines and best practices are virtually the same in ABAP development as in any other language. Assertion should be used as internal guidance checks only, exceptions for regular input validation errors and other stuff. It might be sensible to leave the assertions in the code - after all, you'd probably rather want your program to crash in a controlled fashion than continue in an unforeseen way and probably damage some critical data in the process without anyone noticing. Take a look at checkpoint groups if you don't want your program to abort in a production environment - but in my opinion: What's the use of a sanity check (as a last line of defense) if it's disabled in the environment where it matters most?

Of course I'm assuming that the input is validated properly (so that crashes are prevented) and that all APIs are used according to the intended use and documentation. Unfortunately - as with every other programming language - it's up to the developer to live up to these standards.