TOML Array of Tables ([[table]]) and JSON Arrays of Objects

The array of tables syntax ([[table]]) is one of TOML's most distinctive features. It provides a clean way to define arrays of objects that would otherwise require verbose inline table syntax.

TOML array of tables:

[[products]]
name = "Hammer"
sku = 738594937

[[products]]
name = "Nail"
sku = 284758393
color = "gray"

Converts to JSON:

{
  "products": [
    {
      "name": "Hammer",
      "sku": 738594937
    },
    {
      "name": "Nail",
      "sku": 284758393,
      "color": "gray"
    }
  ]
}

Each [[products]] creates a new element in the products array. All key-value pairs between two [[products]] headers belong to that array element.

Nested arrays of tables:

[[fruits]]
name = "apple"

[[fruits.varieties]]
name = "red delicious"

[[fruits.varieties]]
name = "granny smith"

[[fruits]]
name = "banana"

[[fruits.varieties]]
name = "plantain"

Converts to JSON:

{
  "fruits": [
    {
      "name": "apple",
      "varieties": [
        {"name": "red delicious"},
        {"name": "granny smith"}
      ]
    },
    {
      "name": "banana",
      "varieties": [
        {"name": "plantain"}
      ]
    }
  ]
}

How it works:

1. [[fruits]] appends a new object to the fruits array.
2. [[fruits.varieties]] appends a new object to the varieties array inside the most recently defined fruits element.
3. The next [[fruits]] starts a fresh fruit object with its own varieties array.

When converting JSON to TOML: Any JSON array where every element is an object should be converted to TOML's [[array]] syntax. This is more readable than inline tables for objects with multiple keys.

Comparison with inline tables:

# Inline (compact but hard to read for complex objects)
products = [{name = "Hammer", sku = 738594937}, {name = "Nail", sku = 284758393}]

# Array of tables (readable for complex objects)
[[products]]
name = "Hammer"
sku = 738594937

Use inline tables for simple objects with 1-2 keys, and array of tables for anything more complex.