ligo/gitlab-pages/docs/language-basics/maps-records.md

id	title
maps-records	Maps, Records

So far we've seen pretty basic data types. LIGO also offers more complex built-in constructs, such as Maps and Records.

Maps

Maps are natively available in Michelson, and LIGO builds on top of them. A requirement for a Map is that its keys be of the same type, and that type must be comparable.

Here's how a custom map type is defined:

type ledger is map(address, tez);

type ledger = (address, tez) map

And here's how a map value is populated:

const ledger: ledger = map
    ("tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx": address) -> 1000mutez;
    ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address) -> 2000mutez;
end

Notice the -> between the key and its value and ; to separate individual map entries.

("<string value>": address) means that we type-cast a string into an address.

let ledger: ledger = Map.literal
  [ (("tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx": address), 1000mutez) ;
    (("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address), 2000mutez) ;
  ]

Map.literal constructs the map from a list of key-value pair tuples, (<key>, <value>). Note also the ; to separate individual map entries.

("<string value>": address) means that we type-cast a string into an address.

Accessing map values by key

If we want to access a balance from our ledger above, we can use the [] operator/accessor to read the associated tez value. However, the value we'll get will be wrapped as an optional; in our case option(tez). Here's an example:

const balance: option(tez) = ledger[("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address)];

let balance: tez option = Map.find_opt ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address) ledger

Obtaining a map value forcefully

Accessing a value in a map yields an option, however you can also get the value directly:

const balance: tez = get_force(("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address), ledger);

let balance: tez = Map.find ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address) ledger

Records

Records are a construct introduced in LIGO, and are not natively available in Michelson. The LIGO compiler translates records into Michelson Pairs.

Here's how a custom record type is defined:

type user is record 
    id: nat;
    is_admin: bool;
    name: string;
end

type user = {
  id: nat;
  is_admin: bool;
  name: string;
}

And here's how a record value is populated:

const user: user = record
    id = 1n;
    is_admin = True;
    name = "Alice";
end

let user: user = {
  id = 1n;
  is_admin = true;
  name = "Alice";
}

Accessing record keys by name

If we want to obtain a value from a record for a given key, we can do the following:

const is_admin: bool = user.is_admin;

let is_admin: bool = user.is_admin