48 lines
2.1 KiB
Markdown
48 lines
2.1 KiB
Markdown
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---
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description: ""
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title: The Only Good Thing About YAML: Anchors, Aliases, and Extend
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draft: true
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---
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**TL;DR**: You can prefix a YAML value with `&{NAME_HERE}` (like `&key`) to
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create an anchor with that name and reference it later with `*{NAME_HERE}` (like
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`*key`) to avoid repeating yourself in a document. You can also "merge" object
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values using the `<<` key.
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# Introduction
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Since working at [Postmates][pm] ([we're hiring][pm-referral]!) and getting my
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feet wet in the vast world of Kubernetes, I've had to work with a *lot* of
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[YAML][yaml].
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One of the most important things for me when dealing with YAML was to keep in
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mind is that *YAML is a superset of JSON*. This means all JSON documents are
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valid YAML documents. When you look at YAML, it can be easy as a human to fail
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to parse what's actually going on. Which is fair, since fully parsing a YAML
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document actually requires quite a bit of code, which is a topic unto itself. If
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you remember that a YAML document is really (almost always) just a map of keys
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and values with various shortcuts that allow you the text representation (YAML)
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to look nice, YAML becomes a good deal easier to reason about.
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That also means, though, that YAML is wordy. Not as noisy as JSON, since many of
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the symbols are now unnecessary, but still wordy. If you have a type of object
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with 20 fields, all of which are mostly the same except for a few fields here
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and there, you are going to have to repeat yourself a lot.
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... At least in JSON. While I dislike YAML, I did learn two really neat features
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that helped enormously in cleaning things up and avoiding repetition or needing
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to change things in more than one place. I'm surprised, though, that these
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features occur so infrequently (maybe parser support is lacking?) out in the
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real, wild world as to be nearly undiscoverable: [Anchors and Aliases][aa-spec]
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and the [Merge Key][mk-spec].
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# What is it?
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Basically, in a YAML document, you may denote a value node for future
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referencing later.
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[pm-referral]: https://grnh.se/cc2da77e1
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[yaml]: https://yaml.org/
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[aa-spec]: https://yaml.org/spec/1.2/spec.html#id2765878
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[mk-spec]: https://yaml.org/spec/1.2/spec.html#id2765878
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