YAML Data Types

Master YAML data types including strings, numbers, booleans, arrays, objects, and special values.

Overview of YAML Data Types

YAML supports a rich set of data types that can represent various kinds of information. Understanding these types is crucial for writing effective YAML files.

🔤 Strings

Text data with various formatting options

🔢 Numbers

Integers, floats, and scientific notation

✅ Booleans

True/false values and alternatives

📋 Arrays

Lists and collections of items

🗂️ Objects

Key-value pairs and nested structures

❌ Null

Empty or missing values

Strings

Strings in YAML can be written in multiple ways, each with specific use cases and behaviors.

Basic Strings

# Simple strings (no quotes needed for most cases)
name: John Doe
city: New York
version: 1.0.0

# When quotes are needed
special: "String with : colon"
quoted: "String with spaces and special chars: @#$%"

Quoted Strings

# Double quotes
message: "Hello, World!"
path: "C:\\Users\\John\\Documents"

# Single quotes (no escaping needed inside)
title: 'This is a "quoted" string'
regex: '^[a-zA-Z0-9]+$'

# Escaping in double quotes
escaped: "Line 1\nLine 2\tTabbed"

Multiline Strings

# Literal block scalar (preserves line breaks)
description: |
  This is a multiline string
  that preserves all line breaks
  and formatting exactly as written.

# Folded block scalar (converts to single line)
summary: >
  This is a folded string
  that will be converted
  to a single line with spaces
  between words.

String with Indentation Control

# Strip leading/trailing whitespace
text: |-
  This text has
  no trailing newline

# Keep trailing newline
text: |+
  This text has
  a trailing newline

# Strip leading whitespace
text: |2
    This text has
    indentation stripped

Numbers

YAML supports various number formats including integers, floating-point numbers, and scientific notation.

Integers

# Decimal integers
count: 42
negative: -10
zero: 0

# Octal (base 8)
octal: 0o755

# Hexadecimal (base 16)
hex: 0xFF
color: 0x1A2B3C

# Binary (base 2)
binary: 0b1010

Floating-Point Numbers

# Basic floats
price: 19.99
percentage: 85.5
negative_float: -3.14

# Scientific notation
large: 1.23e+10
small: 1.23e-10
scientific: 6.022e23

# Special float values
infinity: .inf
negative_infinity: -.inf
not_a_number: .nan

Number Examples in Context

server:
  port: 8080
  timeout: 30.5
  max_connections: 1000
  memory_limit: 1.5e9  # 1.5 GB

database:
  version: 13.2
  max_retries: 3
  connection_pool: 0x20  # 32 in hex

Booleans

YAML supports multiple ways to represent boolean values, making it flexible for different use cases.

Standard Boolean Values

# Standard true/false
is_active: true
is_deleted: false
debug_mode: true
production: false

Alternative Boolean Values

# Yes/No
enabled: yes
disabled: no
feature_flag: yes

# On/Off
power: on
maintenance: off
service: on

# All of these are equivalent to true/false
boolean_examples:
  true_values: [true, yes, on, True, Yes, On, TRUE, YES, ON]
  false_values: [false, no, off, False, No, Off, FALSE, NO, OFF]

⚠️ Important Note:

YAML is case-sensitive for boolean values. True and true are different - only lowercase values are recognized as booleans.

Arrays (Lists)

Arrays in YAML can be written in block style (with dashes) or flow style (with brackets).

Block Style Arrays

# Simple list
fruits:
  - apple
  - banana
  - orange

# List of objects
users:
  - name: John
    age: 30
  - name: Jane
    age: 25

# Nested lists
matrix:
  - [1, 2, 3]
  - [4, 5, 6]
  - [7, 8, 9]

Flow Style Arrays

# Inline arrays
colors: [red, green, blue]
numbers: [1, 2, 3, 4, 5]

# Mixed types
mixed: [1, "hello", true, null]

# Nested flow arrays
coordinates: [[1, 2], [3, 4], [5, 6]]

Empty Arrays

# Empty block style
empty_list: []

# Empty flow style
empty_flow: []

# Both are equivalent

Objects (Maps)

Objects in YAML are collections of key-value pairs, similar to dictionaries or hash maps in programming languages.

Block Style Objects

# Simple object
person:
  name: John Doe
  age: 30
  email: john@example.com

# Nested objects
company:
  name: "Acme Corp"
  address:
    street: "123 Main St"
    city: "New York"
    country: "USA"
  employees:
    - name: John
      position: "Developer"
    - name: Jane
      position: "Designer"

Flow Style Objects

# Inline objects
person: {name: John, age: 30, city: New York}

# Nested flow objects
config: {database: {host: localhost, port: 5432}, server: {port: 8080}}

# Mixed with arrays
users: [{name: John, active: true}, {name: Jane, active: false}]

Complex Nested Structure

application:
  name: "My App"
  version: "2.1.0"
  settings:
    database:
      host: localhost
      port: 5432
      credentials:
        username: admin
        password: secret
    features:
      - authentication
      - logging
      - monitoring
    limits:
      max_users: 1000
      timeout: 30

Null Values

YAML provides several ways to represent null or empty values.

Null Value Representations

# Explicit null
value: null

# Tilde notation
empty: ~

# Empty value (no value after colon)
missing:

# All three are equivalent and represent null/undefined

Null in Arrays and Objects

# Null in arrays
items: [apple, null, banana, null]

# Null in objects
user:
  name: John
  middle_name: null
  last_name: Doe
  nickname:  # This is also null

# Mixed null values
data:
  present: "some value"
  missing: null
  empty: ~
  undefined:

Type Coercion and Quoting

YAML automatically detects data types, but sometimes you need to force a specific type using quotes.

Automatic Type Detection

# These are detected as numbers
count: 42
price: 19.99
scientific: 1.23e10

# These are detected as booleans
enabled: true
disabled: false

# These are detected as strings
name: John
version: 1.0.0

Forcing String Type with Quotes

# Force numbers to be strings
zip_code: "12345"  # String, not number
phone: "555-1234"  # String with dashes
version: "2.0"     # String version

# Force booleans to be strings
flag: "true"       # String "true", not boolean true
status: "yes"      # String "yes", not boolean true

# Force null to be string
empty: "null"      # String "null", not null value

Special Values That Need Quoting

# Values that look like other types
date_like: "2023-12-25"     # Looks like date, quote to keep as string
number_like: "123"          # Looks like number, quote to keep as string
boolean_like: "yes"         # Looks like boolean, quote to keep as string
null_like: "null"           # Looks like null, quote to keep as string

# Values with special characters
path: "C:\\Users\\John"     # Backslashes
regex: "^[a-zA-Z]+$"        # Special regex characters
url: "https://example.com"  # Colons and slashes

Practice Exercises

Test your understanding with these practical exercises:

Exercise 1: Mixed Data Types

Create a YAML file representing a product catalog with different data types.

Show Solution 
products:
  - id: 1
    name: "Laptop"
    price: 999.99
    in_stock: true
    tags: [electronics, computer, portable]
    specifications:
      weight: 2.5
      dimensions: [35.5, 24.0, 2.0]
      warranty: "2 years"
    reviews: null

Exercise 2: Configuration File

Create a server configuration with nested objects, arrays, and various data types.

Show Solution 
server:
  name: "Production Server"
  environment: "prod"
  debug: false
  port: 8080
  ssl:
    enabled: true
    certificate: "/etc/ssl/cert.pem"
    key: "/etc/ssl/key.pem"
  databases:
    - name: "users"
      host: "db1.example.com"
      port: 5432
    - name: "logs"
      host: "db2.example.com"
      port: 5432
  features: [auth, logging, monitoring, caching]
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