Changes between Version 29 and Version 30 of DeveloperGuidelines/CodeConventions

Timestamp:

10/09/13 19:43:33 (11 years ago)

Author:

Dominic König

Comment:

--

DeveloperGuidelines/CodeConventions

@@ -121 +121 @@
     f.close()
 }}}
- 
 
+When should you raise Exceptions, anyway?
+
+If it is not possible to continue with the respective processing because there can not be any plausible result, then the necessary consequences highly depend on the cause:
+
+  - You should never raise an exception for '''Validation Errors''' - any invalid user input '''must be caught and properly reported''' back to the client (simply because users can't do anything about an exception, so it would render the functionality unusable - whilst a proper error message may help the user to correct their input). Failure to catch validation errors is always a bug.
+  - '''Configuration Errors''', wherever possible, should at most issue a warning (if the invalid setting is obviously a mistake), and else get ignored and fall back to reasonable defaults. Only if there is no possible fallback action, then Configuration Errors should be treated as Runtime Errors.
+  - '''Runtime Errors''' may raise exceptions if unrecoverable (i.e. if there's no reasonable handling possible at the respective level). However, they must be caught at a higher level and properly reported back to the client in order to explain the reason and allow correction.
+  - '''Programming Errors''' (=bugs) ''must'' lead to exceptions in order to attract immediate attention of the programmer to the bug and help them debugging. They should never be caught unless you intend to implement a plausible fallback action (and even then a warning may be appropriate in most cases).
+
+Eden is an unsupervised server system, so you must have very good reasons to let it crash.
+
+Remember that any uncaught exception leads to a HTTP 500 status with error ticket - and an HTTP 500 status in Eden is a bug by definition. Users can't do anything about error tickets, so the only legitimate reason to raise an uncaught exception in Eden is that you are 100% sure that the error condition leading to the exception is caused by a bug.
 === Nulls ===
 Nulls make code much more complicated by introducing special cases that require special null-checking logic in every client, making code harder to understand and maintain. They often and easily cause hard-to-diagnose errors.