YAML Tags

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YAML tags are powerful features that provide explicit type information and custom data handling in YAML documents. They allow users to define and interpret data beyond YAML's basic types.

Purpose of YAML Tags

Tags serve several crucial functions in YAML:

Specify data types explicitly
Enable custom data representations
Facilitate language-specific object serialization
Enhance interoperability between different systems

Tag Syntax

YAML tags use the following syntax:

!!tag_name value

The double exclamation marks (!!) indicate a global tag, while a single exclamation mark (!) denotes a local tag.

Common YAML Tags

YAML provides several built-in tags for common data types:

!!str: String
!!int: Integer
!!float: Floating-point number
!!bool: Boolean
!!null: Null value
!!seq: Sequence (list)
!!map: Mapping (dictionary)

Examples

Basic Tag Usage

age: !!int "42"
pi: !!float "3.14159"
is_valid: !!bool "true"
names: !!seq
  - Alice
  - Bob
  - Charlie
person: !!map
  name: John Doe
  age: 30

Custom Tags

Users can define custom tags for specific data types or objects:

%TAG !obj! tag:example.com,2023:
---
myObject: !obj!CustomClass
  property1: value1
  property2: value2

Tag Resolution

YAML parsers use tag resolution to determine how to interpret tagged data. This process involves:

Identifying the tag
Locating the corresponding schema
Applying the schema to construct the appropriate data type or object

Best Practices

Use tags judiciously to maintain readability
Prefer implicit typing when possible
Document custom tags thoroughly
Ensure tag compatibility across systems

Related Concepts

To deepen your understanding of YAML and its features, explore these related topics:

By mastering YAML tags, you'll enhance your ability to create precise and flexible YAML documents, improving data representation and interoperability in your projects.