[twic]

I follow Joe Duffy in recognising that we should make a distinction between "errors" and "bugs" [0]. IOException is an error; out of bounds access, division by zero, assertion failures, and things like ClassCastException and NullPointerException in Java, are bugs.

For errors, you should do error handling, which means you want the compiler to make sure you don't miss them.

For bugs, you want to let the program bomb out, either aborting entirely or stopping at some high-level boundary from which it's possible to sanely continue. In Java, unchecked exceptions are a mostly adequate mechanism for that. Rust's catch_unwind is better, because it makes stronger guarantees [1]. Erlang's approach of terminating the thread and throwing away its heap is also very good, if you can apply that.

[0] http://joeduffyblog.com/2016/02/07/the-error-model/#bugs-are...

[1] https://doc.rust-lang.org/std/panic/fn.catch_unwind.html

[eeereerews]

But once you've accepted unchecked exceptions (and paid the cost of the having them), it just doesn't make sense to only use them only for bugs. For example, it is better to

  try:
    x = json['foo']['bar'][i]
  catch OOB:
    handle error

than to

  if not (json is a dict and
          'foo' in json and
          json['foo'] is a dict and
          ...):
    handle error
  x = json['foo']['bar'][i]

even though in the former, unchecked exceptions are used for non-bugs.

[nicoburns]

The idea is that for bugs you don't even need a try-catch (or maybe one around your entire program). And pattern matching and functions like `map` make the second case much nicer.