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Your First Coin

This tutorial introduces how you can compile, deploy, and mint your own coin, named MoonCoin.

Step 1: Pick an SDK​

Install your preferred SDK from the below list:

Step 2: Install the CLI​

Install the precompiled binary for the Aptos CLI.

Step 3: Run the example​

Clone the aptos-core repo:

git clone https://github.com/aptos-labs/aptos-core.git

Navigate to the TypeScript SDK directory:

cd ~/aptos-core/ecosystem/typescript/sdk

Install the necessary dependencies:

pnpm install

Run the TypeScript your_coin example:

cd examples/typescript
pnpm your_coin ~/aptos-core/aptos-move/move-examples/moon_coin

Step 3.1: Build the package​

The example run will pause with the following output:

=== Addresses ===
Alice: 0x5e603a89cf690d7134cf2f24fdb16ba90c4f5686333721c12e835fb6c76bc7ba
Bob: 0xc8421fa4a99153f955e50f1de2a6acff2f3fd0bb33aa17ba1f5b32b699f6c825

Update the package with Alice's address, compile, and press enter.

At this point, open another terminal and change directories to the MoonCoin package's directory:

cd ~/aptos-core/aptos-move/move-examples/moon_coin

Next, build the package using the CLI:

aptos move compile --named-addresses MoonCoin=0x5e603a89cf690d7134cf2f24fdb16ba90c4f5686333721c12e835fb6c76bc7ba --save-metadata

The --named-addresses is a list of address mappings that must be translated in order for the package to be compiled to be stored in Alice's account. Notice how MoonCoin is set to Alice's address printed above. Also --save-metadata is required to publish the package.

Step 3.2: Completing the example​

Returning to the previous prompt, press ENTER as the package is now ready to be published.

The application will complete, printing:


Publishing MoonCoin package.

Bob registers the newly created coin so he can receive it from Alice.
Bob's initial MoonCoin balance: 0.
Alice mints Bob some of the new coin.
Bob's updated MoonCoin balance: 100.

Step 4: MoonCoin in depth​

Step 4.1: Building and publishing the MoonCoin package​

Move contracts are effectively a set of Move modules known as a package. When deploying or upgrading a new package, the compiler must be invoked with --save-metadata to publish the package. In the case of MoonCoin, the following output files are critical:

  • build/Examples/package-metadata.bcs: Contains the metadata associated with the package.
  • build/Examples/bytecode_modules/moon_coin.mv: Contains the bytecode for the moon_coin.move module.

These are read by the example and published to the Aptos blockchain:

const modulePath = process.argv[2];
const packageMetadata = fs.readFileSync(path.join(modulePath, "build", "Examples", "package-metadata.bcs"));
const moduleData = fs.readFileSync(path.join(modulePath, "build", "Examples", "bytecode_modules", "moon_coin.mv"));

console.log("Publishing MoonCoin package.");
let txnHash = await client.publishPackage(alice, new HexString(packageMetadata.toString("hex")).toUint8Array(), [
  new TxnBuilderTypes.Module(new HexString(moduleData.toString("hex")).toUint8Array()),
]);
await client.waitForTransaction(txnHash, { checkSuccess: true });

Step 4.2: Understanding the MoonCoin module​

The MoonCoin module defines the MoonCoin struct, or the distinct type of coin type. In addition, it contains a function called init_module. The init_module function is called when the module is published. In this case, MoonCoin initializes the MoonCoin coin type as a ManagedCoin, which is maintained by the owner of the account.

ManagedCoin framework

ManagedCoin is a simple coin management framework for coins directly managed by users. It provides convenience wrappers around mint and burn.

module MoonCoin::moon_coin {
    struct MoonCoin {}

    fun init_module(sender: &signer) {
        aptos_framework::managed_coin::initialize<MoonCoin>(
            sender,
            b"Moon Coin",
            b"MOON",
            6,
            false,
        );
    }
}

Step 4.3: Understanding coins​

Coins have several primitives:

  • Minting: Creating new coins.
  • Burning: Deleting coins.
  • Freezing: Preventing an account from storing coins in CoinStore.
  • Registering: Creating a CoinStore resource on an account for storing coins.
  • Transferring: Withdrawing and depositing coins into CoinStore.
tip

The entity that creates a new coin gains the capabilities for minting, burning, and freezing.

Step 4.3.1: Initializing a coin​

Once a coin type has been published to the Aptos blockchain, the entity that published that coin type can initialize it:

public fun initialize<CoinType>(
    account: &signer,
    name: string::String,
    symbol: string::String,
    decimals: u8,
    monitor_supply: bool,
): (BurnCapability<CoinType>, FreezeCapability<CoinType>, MintCapability<CoinType>) {
    let account_addr = signer::address_of(account);

    assert!(
        coin_address<CoinType>() == account_addr,
        error::invalid_argument(ECOIN_INFO_ADDRESS_MISMATCH),
    );

    assert!(
        !exists<CoinInfo<CoinType>>(account_addr),
        error::already_exists(ECOIN_INFO_ALREADY_PUBLISHED),
    );

    let coin_info = CoinInfo<CoinType> {
        name,
        symbol,
        decimals,
        supply: if (monitor_supply) { option::some(optional_aggregator::new(MAX_U128, false)) } else { option::none() },
    };
    move_to(account, coin_info);

    (BurnCapability<CoinType>{ }, FreezeCapability<CoinType>{ }, MintCapability<CoinType>{ })
}

This ensures that this coin type has never been initialized before. Notice the check on lines 10 and 15 to ensure that the caller to initialize is the same one that actually published this module, and that there is no CoinInfo stored on their account. If both those conditions check, then a CoinInfo is stored and the caller obtains capabilities for burning, freezing, and minting.

tip

MoonCoin calls this initialize function automatically upon package publishing.

Step 4.3.2: Registering a coin​

To use a coin, an entity must register a CoinStore for it on their account:

public entry fun registerCoinType(account: &signer) {

MoonCoin uses ManagedCoin that provides an entry function wrapper: managed_coin::register. Here is an example script for registration:

script {
    fun register(account: &signer) {
        aptos_framework::managed_coin::register<MoonCoin::moon_coin::MoonCoin>(account)
    }
}

Step 4.3.3: Minting a coin​

Minting coins requires the mint capability that was produced during initialization. the function mint (see below) takes in that capability and an amount, and returns back a Coin<T> struct containing that amount of coins. If the coin tracks supply, it will be updated.

public fun mint<CoinType>(
    amount: u64,
    _cap: &MintCapability<CoinType>,
): Coin<CoinType> acquires CoinInfo {
    if (amount == 0) {
        return zero<CoinType>()
    };

    let maybe_supply = &mut borrow_global_mut<CoinInfo<CoinType>>(coin_address<CoinType>()).supply;
    if (option::is_some(maybe_supply)) {
        let supply = option::borrow_mut(maybe_supply);
        optional_aggregator::add(supply, (amount as u128));
    };

    Coin<CoinType> { value: amount }
}

ManagedCoin makes this easier by providing an entry function managed_coin::mint.

Step 4.3.4: Transferring a coin​

Aptos provides several building blocks to support coin transfers:

  • coin::deposit<CoinType>: Allows any entity to deposit a coin into an account that has already called coin::register<CoinType>.
  • coin::withdraw<CoinType>: Allows any entity to extract a coin amount from their account.
  • aptos_account::transfer_coins<CoinType>: Transfer coins of specific CoinType to a receiver.
important

There are two separate withdraw and deposit events instead of a single transfer event.

Supporting documentation​