FA2 tokens

ligo/fa library provides :

• the interface and types defined by FA2 (TZIP-12)
• a LIGO implementation for :
  • unique NFTs: This contract implements the FA2 interface for NFT(non-fungible-token) where a token can belong to only one address at a time (1:1)
  • Single Assets: This is an implementation of Single Asset Token where a different amount of single token can belong to multiple addresses at a time (1:n)
  • Multiple Assets: This is an implementation of Multi Asset Token where there are several token ids (available in different amounts) and they can belong to multiple addresses (m:n)

Use the implementation directly

The library provides you 3 template implementations ready to deploy

1. To install this package, run ligo install @ligo/fa. It will download the files
2. Deploy the NFT contract with Taquito the Ghostnet with alice wallet

make compile
make deploy

Extend an implementation

If you need additional features in your contract, you can use the extendable version. An example is available in the file examples/mintable.mligo. Using the extension mechanism, it adds an admin address to the storage, as well as a mint entrypoint to mint owner-less NFTs. Only the admin can call this entrypoint.

Install the library and create a new file

ligo install @ligo/fa
touch mintable.mligo

To extend the storage, define the type of the extension and refer to the original storage type as such:

#import "@ligo/fa/lib/main.mligo" "FA2"

module NFT = FA2.NFTExtendable

type extension = {
  admin: address
}

type storage = extension NFT.storage
type ret = operation list * storage

Importing the library allows you to refer to the TZIP12 operations signatures and make it easier to redefine all the entrypoints and views that are required:

(* Standard FA2 interface, copied from the source *)

[@entry]
let transfer (t: NFT.TZIP12.transfer) (s: storage) : ret =
  NFT.transfer t s

[@entry]
let balance_of (b: NFT.TZIP12.balance_of) (s: storage) : ret =
  NFT.balance_of b s

(* Etc. *)

To make it easier to define new entrypoints, some functions are available in the library, and you can also use the storage fields directly:

(* Extension *)

type mint = {
   owner    : address;
   token_id : nat;
}

[@entry]
let mint (mint : mint) (s : storage): ret =
  let sender = Tezos.get_sender () in
  let () = assert (sender = s.extension.admin) in
  let () = NFT.Assertions.assert_token_exist s.token_metadata mint.token_id in
  (* Check that nobody owns the token already *)
  let () = assert (Option.is_none (Big_map.find_opt mint.token_id s.ledger)) in
  let s = NFT.set_balance s mint.owner mint.token_id in
  [], s

Note that this version requires the minted NFTs to be already defined in the token_metadata big map. However, you can also change the mint entrypoint to create new tokens dynamically.

Implement the interface differently

If you are not happy with the default NFT implementation, you can define your own

Create a new file

touch myTzip12NFTImplementation.jsligo

Import some code and define implementation of missing types ledger and operators

#import "@ligo/fa/lib/fa2/common/errors.mligo" "Errors"

#import "@ligo/fa/lib/fa2/common/assertions.jsligo" "Assertions"

#import "@ligo/fa/lib/fa2/common/tzip12.datatypes.jsligo" "TZIP12"

#import "@ligo/fa/lib/fa2/common/tzip12.interfaces.jsligo" "TZIP12Interface"

#import "@ligo/fa/lib/fa2/common/tzip16.datatypes.jsligo" "TZIP16"

export namespace NFT implements TZIP12Interface.FA2{
    export type ledger = big_map<nat, address>;
    type operator = address;
    export type operators = big_map<[address, operator], set<nat>>;
    export type storage = {
        ledger: ledger,
        operators: operators,
        token_metadata: TZIP12.tokenMetadata,
        metadata: TZIP16.metadata
    };
    type ret = [list<operation>, storage];

}

Copy the missing entrypoints from the TZIP12 interface and give your own implementation

  @entry
    const transfer = (p: TZIP12.transfer, s: storage): ret => {
        failwith("TODO");
    };
    @entry
    const balance_of = (p: TZIP12.balance_of, s: storage): ret => {
        failwith("TODO");
    };
    @entry
    const update_operators = (p: TZIP12.update_operators, s: storage): ret => {
        failwith("TODO");
    };

Compile it (do not forget to add the parameter -m NFT as you have to define a namespace to be able to implement an interface)

ligo compile contract myTzip12NFTImplementation.jsligo -m NFT