Is there YAML syntax for sharing part of a list or map?

Question

So, I know I can do something like this:

sitelist: &sites
  - www.foo.com
  - www.bar.com

anotherlist: *sites

And have sitelist<

Answer 1

As the previous answers have pointed out, there is no built-in support for extending lists in YAML. I am offering yet another way to implement it yourself. Consider this:

defaults: &defaults
  sites:
    - www.foo.com
    - www.bar.com

setup1:
  <<: *defaults
  sites+:
    - www.baz.com

This will be processed into:

defaults:
  sites:
    - www.foo.com
    - www.bar.com

setup1:
  sites:
    - www.foo.com
    - www.bar.com
    - www.baz.com

The idea is to merge the contents of a key ending with a '+' to the corresponding key without a '+'. I implemented this in Python and published here.

Enjoy!