Print POSIX character class

Given a class, such as

[:digit:]

I would like the output to be

0123456789

Note, the method should work for all POSIX character classes. Here is what I have tried

$ printf %s '[:digit:]'
[:digit:]

§ Character classes

$ seq 126 | awk '{printf "%c", $0}' | grep -o '[[:digit:]]'
0
1
2
3
4
5
6
7
8
9