Populating an array from a select statement

What's the most straightforward way to populate an array from a select
statement? For example, using a fictional extension of SQL syntax, I'd like:

update users set emails=ARRAY[select email from address where userid=25]
where id=25;

So if user 25  has emails john@domain.com, john@gmail.com, and
john@yahoo.com in the address table,
select emails from user where id=25;
will return:
                                          emails
----------------------------------------------------------------
 {john@domain.com, john@gmail.com, and john@yahoo.com}


If there's no built in way to do this, I'd suggest it as a future feature.