A struct type is the type denoted by the name of an struct item. A struct type is a heterogeneous product of other types, called the fields of the type.

New instances of a struct can be constructed with a struct expression.

Struct types are either stored in storage or memory but are never stored directly on the stack.

Examples:

struct Rectangle:
  width: u256
  length: u256

contract Example:
  # A Rectangle in storage
  area: Rectangle

  fn do_something():
    let length: u256 = 20
    # A rectangle in memory
    let square: Rectangle = Rectangle(width: 10, length)

All fields of struct types are always initialized.

The data layout of a struct is not part of its external API and may be changed in any release.

The fields of a struct may be qualified by visibility modifiers, to allow access to data in a struct outside a module.