I have a doubt about the usage if dash.

I know from different books and writings that double dash is used to set off

All of my friends-Bob, Jeffrey, Jason, and Brett-did well in college.

=> Here, double dash is working just like non-essential modifier. The words between dashes do not interrupt the grammar of the sentence.

There is no way--and no particular reason--to gauge popular interest in such an approach.

What is the rule about single dash?

Can we use a clause after single dash?

Thanks.