Merge Key Language-Independent Type for YAML™ Version 1.1

Working Draft 2005-01-18

Oren Ben-Kiki

Clark Evans

Brian Ingerson

This document may be freely copied provided it is not modified.


This specification is a draft reflecting consensus reached by members of the yaml-core mailing list. Any questions regarding this draft should be raised on this list.







N/A (single format).




Specify one or more mappings to be merged with the current one.

The “<<” merge key is used to indicate that all the keys of one or more specified maps should be inserted into the current map. If the value associated with the key is a single mapping node, each of its key/value pairs is inserted into the current mapping, unless the key already exists in it. If the value associated with the merge key is a sequence, then this sequence is expected to contain mapping nodes and each of these nodes is merged in turn according to its order in the sequence. Keys in mapping nodes earlier in the sequence override keys specified in later mapping nodes.

Example 1. !!merge Examples

- &CENTER { x: 1, y: 2 }
- &LEFT { x: 0, y: 2 }
- &BIG { r: 10 }
- &SMALL { r: 1 }

# All the following maps are equal:

- # Explicit keys
  x: 1
  y: 2
  r: 10
  label: center/big

- # Merge one map
  << : *CENTER
  r: 10
  label: center/big

- # Merge multiple maps
  << : [ *CENTER, *BIG ]
  label: center/big

- # Override
  << : [ *BIG, *LEFT, *SMALL ]
  x: 1
  label: center/big