DataMapper properties are simply Ruby methods that DM makes for you (they are made using Ruby's meta-programming features when the property
method is called). You could try
p user.methods.sort - Object.methods
to get a listing of properties on the User
object you created.
DM will have chosen to make the method user.confirmed?
for the :confirmed
property - it follows a loose Ruby convention of naming boolean methods with a ?
on the end. I have checked this by exploring the DataMapper code here: https://github.com/datamapper/dm-core/blob/master/lib/dm-core/property.rb