Today I encountered some strange behaviour when using the [ArrayElementType] tag. I had a piece of code which looked like this:

package {
	import mx.collections.ArrayCollection;
	[Bindable]
	public class MetaData {
		public var ac:ArrayCollection
		[ArrayElementType("nl.flexperiments.test.TestObject")]
		public var ac2:ArrayCollection;
	}
}

Every time I tried to compile, Flex Builder (2.01 that is) gave an ‘Internal Build Error’. The error disappeared when I removed the ArrayElementType metadata, so I thought there was something wrong in my class nl.flexperiments.test.TestObject, but couldn’t find anything. Then I found out that the problem was not the metatag, but the line preceding it. Because Actionscript isn’t really strict in closing your lines with a semi colon, you sometimes forget it. So did I (line 5 of the example isn’t properly closed).

It turns out that Flex Builder (2) can give some strange behavior when you don’t close your lines in combination with MetaData tags.

This evening, I tried to reproduce it with Flex Builder 3, but couldn’t, it’s a bug in the FB2.0.1 compiler.

Bottom line: always use a semi-colon to close your actionscript lines, it spares you a headache!