Trans some Java code to D, so far has lots of issues, this time I will focus on Exception.

interface Widget {
	string name();
}

Widget createWidget() {
	return null;
}

void test() {
	createWidget().name();
}

The similar code in Java will throw NullPointerException, but in D it
will throw object.Error, how do I know it was caused by null?

And is it possible to override callback like onOutOfMemoryError & onRangeError?

In Java you can catch multi exception like

try {
	...
} catch (A | B e) {
	...
}

can trans to:
try {
	...
} catch (A e) {
	...
} catch (B e) {
	...
}

or:
try {
	...
} catch (Throwable t) {
	if (t is A | B) {
		...
	} else {
		throw t;
	}
}

which one is better, will it has side effect?

On 9/23/20 12:53 PM, webdev wrote:
> Trans some Java code to D, so far has lots of issues, this time I will focus on Exception.
> 
> interface Widget {
>      string name();
> }
> 
> Widget createWidget() {
>      return null;
> }
> 
> void test() {
>      createWidget().name();
> }
> 
> The similar code in Java will throw NullPointerException, but in D it
> will throw object.Error, how do I know it was caused by null?

No null pointer exceptions in D (you can get them on Linux, but by enabling a non-portable feature of the runtime).

D relies on segfault to halt your program. In debug mode, on some platforms, it might throw an Error (I think on Windows only).

Null pointer dereferences are considered a programming error and not recoverable. Do not try to catch an Error.

> And is it possible to override callback like onOutOfMemoryError & onRangeError?

I believe if you define these functions extern(C) in your app they will be used.

> In Java you can catch multi exception like
> 
> try {
>      ...
> } catch (A | B e) {
>      ...
> }
> 
> can trans to:
> try {
>      ...
> } catch (A e) {
>      ...
> } catch (B e) {
>      ...
> }
> 
> or:
> try {
>      ...
> } catch (Throwable t) {
>      if (t is A | B) {
>          ...
>      } else {
>          throw t;
>      }
> }
> 
> which one is better, will it has side effect?

1. Don't catch Throwable, as Errors should not be caught. Catch Exception instead
2. Your code should work as expected I think. You can rethrow exceptions.

-Steve

On Wednesday, 23 September 2020 at 16:53:05 UTC, webdev wrote:
> Trans some Java code to D, so far has lots of issues,

Please, use the learn forum for stuff like this.