DConf 2026 in London

I would classify D's scope exit/failure/success as RAII actually, even if D uses a GC.

Sometimes you might not need exceptions and something like std::expected or optional is better.

In my case I use expected for some network APIs since I expect failures to happen out of my control aspart of the flow of my program, but I do not see why I would not use exceptions in many other situations, such as for non-ignorsble errors. I could think of a lack of disk space or some other fatal error thst is not under the control of the program.

If you forget to handle this, the error will cascade.

Also, exceptions do not make the signature of a function change (at least not in C++, Java checked exceptions is different). This means that the plasticity for adding errors at any depth of the call stack augments without bypassing any error silently.

All in all, I would say exceptions should be the main mechanism in normal circumstances and for expected errors you csn use error/result types.

Standard exception handling is:

- Whenever an error happens, the program puts a description of it into an “exception” object. You go from the innermost dynamic scope to the outermost looking for handlers. Once you find a handler willing to accept that type of exception, you unwind to the point where it was installed then invoke it, passing the exception object.

Condition handling[3] is:

- Whenever an error happens, the program puts a description of it into a “condition” object. You go from the innermost dynamic scope to the outermost looking for handlers. Once you find a condition handler willing to accept that type of condition, you invoke it as a regular callback, without unwinding, passing the condition object.

- The handler then packs up some data into a “restart” object. You go through all the dynamic scopes again (remember that the erroring function is still active). Once you find a restart handling willing to accept this type of restart, you unwind to the point where it was installed then invoke it, passing the restart object.

(I am omitting things outside the happy path: a way for the exception/condition handler to punt, what happens if the condition handler does not invoke a restart, etc.)

As far as the benefits of this two-phase approach, Practical Common Lisp gives an example[4] of a single-record parser that raises an “invalid record” condition, a loop around it that installs a “skip to next record” restart, and finally the caller can make the policy decision on what to do for invalid records.

As another example, Common Lisp signals an “unbound-variable”[5] condition leaving the “use-value” and “store-value” restarts in scope, then the REPL installs a handler that offers them interactively. (My own half-serious example of a DOS abort/retry/fail prompt is in this vein too, chosen mostly because it feels strange that you can’t do it in a conventional exception system.)

[1] https://package.opendylan.org/dylan-programming-book/excepti...

[2] https://news.ycombinator.com/item?id=31196046

[3] https://www.nhplace.com/kent/Papers/Condition-Handling-2001....

[4] https://gigamonkeys.com/book/beyond-exception-handling-condi...

[5] https://www.lispworks.com/documentation/HyperSpec/Body/e_unb...

By the way, big fan of D even though I don't get to use it much. Appreciate your work!

You might say if it is so easy, why not do it upstream? It takes years of political arguments and random ghosting to get anything done up there, all while constant (regression inducing) code churn breaks your PRs every other month, so you spend 3x the time rebasing than you ever spent writing the implementation before it is merged...... if it ever gets merged at all. I have several successful contributions to upstream D, it happens, but most the work done there is ignored. You might get some encouraging forum replies, but when it comes time to ship it? Crickets. Several former D contributors jumped ship for Zig many years ago, and it was a real loss for us (and real gain for them).

With the opend, I know if it works and delivers real world value, I can ship a release, dmd and ldc together, so minimal duplicated waste work.

What should you use? idk, opend is basically my pet project, provided in the hope that it will be useful, but THIS SOFTWARE IS PROVIDED `'AS IS″ AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE so your mileage may vary. Still, I maintain about a half million lines of code, some of which is quite old, so keeping some stability is important to me while moving forward with select common-sense, incremental improvements. Most D code works fine either way though, I've done web programming a long time, in the old school tradition, so words like "progressive enhancement" and "graceful degradation" are meaningful to me, even when being a compiler maintainer.

    int foo() { return bar(); }

    int bar() { return 3; }