Comments on Scala Blog: 'Application' trait considered harmful

Author the best! Thank you! люстры

Just for the record: Scala 2.9 will fix the behavi...

2011-02-19T13:25:42.769-08:00

Just for the record: Scala 2.9 will fix the behavior of Application.

No. And I think the transition from Hello World pr...

2008-07-26T16:07:00.000-07:00

No. And I think the transition from Hello World programs to real applications shouldn't have to be either! What you're proposing is basically saying "Here, you know that thing we showed you how to use while you were learning? It's actually totally unsafe to use for anything non-trivial". Additionally, it doesn't seem to have any pedagogical value over using the script runner.

Often one just wants to put code in the main entry point to one's application. Sure, you can do all sorts of things to avoid that so you can use Application, but at that point you're doing more work than just "wrap it in a main method".

The bugs caused by Application are non-obvious and completely undocumented. I know of at least two people who have wasted substantial amounts of time trying to figure them out. It has such a narrow scope of utility and can cause such unpleasant problems that leaving it in as an aid to beginners (when really we should be telling the beginners to run screaming from it) is a completely ridiculous idea.

You think "hello, world" programs should be concer...

2008-07-26T15:17:00.000-07:00

You think "hello, world" programs should be concerned about gritty details of JVM thread safety, class initialisers, and hot spot optimisation.?

@antony,

Does it makes sense to teach new ...

2008-07-26T08:20:00.000-07:00

@antony,

Does it makes sense to teach new people a solution which has downsides that are so subtle? I mean, most solutions have trade-offs. But when it's something you learn while you're still mastering "hello, world" you probably aren't ready to understand the gritty details of JVM thread safety, class initializers, and hot spot optimization.

The Application trait idea is salvageable, I think. But as it stands right now it needs to come with at least a big fat warning label in the documentation and probably even a deprecation until it can be fixed or dropped.

"it comes with many severe and hidden pitfalls. Ho...

2008-07-26T00:43:00.000-07:00

"it comes with many severe and hidden pitfalls. Hopefully it will be removed from the standard library, or at least deprecated. In the meantime, save yourself the headache and avoid Application in your applications."

Oh please! It serves it's purpose beautifully! Just don't do any thing that isn't simple inside that class! Just simply use it to bootstrap your application once it gets anything more complicated than a few lines...

1) Who cares if it breaks concurrency! Just don't use it as an entry point where multiple threads could enter. It's only meant as a simple static entry point for you program.

2) Who cares about performance for a simple boot strap code???

In what situation do you really see this causing harm? In the only use case you mention - teaching Scala to people - it's perfect!