YAML: Share values using alias.

23 July 2018 — Written by Mitesh Patel

In YML often we use common values again and again for different purpose. For example, imagine the variation for image_styles for an e-commerce site and most places we use the same style for instance. There's a way to avoid duplication in yml. i.e.

image_style:
  slider:
    width: 780
    height: 550
  teaser:
    width: 100
    height: 150
  carousel:
    width: 100
    height: 150
  main:
    width: 500
    height: 700
  fullscreen:
    width: 500
    height: 700

We are using the same value again for different keys. to avoid this we can give that key an alias (a string starting with &) and we refer that whenever needed by using asterisk (*) sign before the alias, like.

image_style:
  slider:
    width: 780
    height: 550
  teaser: &common_teaser
    width: 100
    height: 150
  carousel:
    <<: *common_teaser
  main: &full_image
    width: 500
    height: 700
  fullscreen:
    <<: *full_image

We can also add extra keys, and modify existing value in the alias when needed.

image_style:
  slider:
    width: 780
    height: 550
  teaser: &common_teaser
    width: 100
    height: 150
  carousel:
    <<: *common_teaser
  main: &full_image
    width: 500
    height: 700
  fullscreen:
    <<: *full_image
    height: 600
    padding: 10

For a simple key-value yml file it will look like,

- &test_data
  - 1
  - 2
- a
- b
- *test_data

which will output

array(array(1, 2), a, b, array(1, 2))

we can also refer multiple aliases for a key:

foo: &foo
  a: alpha
  b: beta
bar: &bar [1, 2, 3, 4]
check:
  <<:
    - *foo
    - *bar
check2:
  <<: [*foo , *bar]

both check and check2 returns the same output.

array(
  'foo' => array('a' => 'alpha', 'b' => 'beta'),
  'bar' => array(1, 2, 3, 4),
  'check' => array('a' => 'alpha', 'b' => 'beta', 0 => 1, 1 => 2, 2 => 3, 3 => 4),
  'check2' => array('a' => 'alpha', 'b' => 'beta', 0 => 1, 1 => 2, 2 => 3, 3 => 4),
)