Attribute by selection node

There are so many nodes similar to this, it seems silly that there isn't a node for this.

Let me explain.

You have a boolean selection of parts of your geometry, and all you want to know is the indexes of the selected geometry. Right now, I wouldn't even know where to start with this.

The closest thing we have to this is the selection input for the attribute statistic node, but the attribute statistic node does not allow you to continue the attribute afterwards, you can only get statistics about that attribute.

So, perhaps an attribute output from the attribute statistic node, then?

It would make things so much quicker and simpler to have something like the sample index node, but instead of the index, you have a selection.

Perhaps I'm missing an easy solution that already exists but as of right now I can't find any easy way to do this.