Composite Types

Structured types

Often contracts require complex data structures, which in turn require well-typed storage or functions to work with. LIGO offers a simple way to compose simple types into structured types.

The first of those structured types is the record, which aggregates types as fields and indexes them with a field name. In the example below you can see the definition of data types for a ledger that keeps the balance and number of previous transactions for a given account.

// Type aliasing

type account = address;
type number_of_transactions = nat;

// The type account_data is a record with two fields.

type account_data = {
  balance: tez,
  transactions: number_of_transactions
};

// A ledger is a map from accounts to account_data

type ledger = map <account, account_data>;

const my_ledger : ledger =
  Map.literal(list([
    ["tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx" as address,
     {balance: 10mutez, transactions: 5n}]]));

Complementary to records are the variant types, which are described in the section on pattern matching. Records are a product of types, while variant types are sums of types.