Coin Introduction

How to define Coin

It is defined in Rooch using the Coin structure, which is a generic structure. We can pass different CoinTypes to it to define different tokens. For example, Coin<USDT>, Coin<USDC>, etc. can be regarded as a container.

Our main concern is CoinType, which can have different abilities, allowing different modules to have different control permissions.

CoinType must have key ability. At this time, it is private and Coin can only be operated within the module where CoinType is defined.
When the store ability is added to CoinType, it becomes public. At this time, in addition to the modules that define CoinType, coin functions can also be operated.

When defining Coin, we register a certain Coin through CoinInfo. CoinInfo is a globally stored object that contains 5 fields.

coin_type: defines the type of Coin.
name: defines the name of Coin.
symbol: Defines the symbol of the token.
decimals defines the precision of the token. Because there are no decimals in Move, we must use precision to convert so that users can see Coin in decimal form.
supply: Define the total amount of tokens.

How to use coins

Use public type Coin

This example will demonstrate the use of having a public type Coin.

module coins::fixed_supply_coin {
    use std::string;
    use moveos_std::signer;
    use moveos_std::object::{Self, Object};
    use rooch_framework::coin;
    use rooch_framework::coin_store::{Self, CoinStore};
    use rooch_framework::account_coin_store;
    const TOTAL_SUPPLY: u256 = 210_000_000_000u256;
    const DECIMALS: u8 = 1u8;
    // The `FSC` CoinType has `key` and `store` ability.
    // So `FSC` coin is public.
    struct FSC has key, store {}
    // construct the `FSC` coin and make it a global object that stored in `Treasury`.
    struct Treasury has key {
        coin_store: Object<CoinStore<FSC>>
    }
    fun init() {
        let coin_info_obj = coin::register_extend<FSC>(    
            string::utf8(b"Fixed Supply Coin"),
            string::utf8(b"FSC"),
            DECIMALS,
        );
        // Mint the total supply of coins, and store it to the treasury
        let coin = coin::mint_extend<FSC>(&mut coin_info_obj, TOTAL_SUPPLY);
        // Frozen the CoinInfo object, so that no more coins can be minted
        object::to_frozen(coin_info_obj);
        let coin_store_obj = coin_store::create_coin_store<FSC>();
        coin_store::deposit(&mut coin_store_obj, coin);
        let treasury_obj = object::new_named_object(Treasury { coin_store: coin_store_obj });

        // Make the treasury object to shared, so anyone can get mutable Treasury object
        object::to_shared(treasury_obj);
    }
    /// Provide a faucet to give out coins to users
    /// In a real world scenario, the coins should be given out in the application business logic.
    public entry fun faucet(account: &signer, treasury_obj: &mut Object<Treasury>) {
        let account_addr = signer::address_of(account);
        let treasury = object::borrow_mut(treasury_obj);
        let coin = coin_store::withdraw(&mut treasury.coin_store, 10000);
        account_coin_store::deposit(account_addr, coin);
    }
}

Define the TOTAL_SUPPLY constant to set the total supply of FSC, and define DECIMALS to set the precision value.

The FSC structure defines the type of token. When defining the type, you do not need to pass any fields, you only need to control the capabilities it possesses.

The Treasury structure defines the treasury of the token, which contains the CoinStore object. This object contains information about the FSC token: token name, token balance, and whether it is frozen.

The init function defines some logic for issuing FSC tokens:

First, create the meta-information of the FSC token through the register_extend function, including: token type, token name, token symbol, token precision, and total token supply (the default initialization value of this function is 0).
Then, use the mint_extend function to mint the token. After the mint is completed, use the to_frozen function to freeze the coin_info_obj object, which means the minting rights are frozen and the tokens cannot be minted.
The create_coin_store function creates a CoinStore object for the FSC token.
The deposit function deposits the tokens just minted into the Balance of CoinStore.
Finally, put the CoinStore object into the treasury and turn the treasury object into a shared object.

The faucet function contains the logic of distributing tokens in the treasury to accounts. This function is only used for development and testing.

Use private type Coin

This example introduces the usage of the private type Coin.

module coins::private_coin {

    use std::string;
    use moveos_std::signer;
    use moveos_std::object::{Self, Object};
    use rooch_framework::coin::{Self, Coin, CoinInfo};
    use rooch_framework::coin_store::{Self, CoinStore};
    use rooch_framework::account_coin_store;

    const ErrorTransferAmountTooLarge: u64 = 1;

    /// This Coin has no `store` ability, 
    /// so it can not be operate via `account_coin_store::transfer`, `account_coin_store::deposit` and `account_coin_store::withdraw`
    struct PRC has key {}

    struct Treasury has key {
        coin_store: Object<CoinStore<PRC>>
    }

    fun init() {
        let coin_info_obj = coin::register_extend<PRC>(
            string::utf8(b"Private Coin"),
            string::utf8(b"PRC"),
            1,
        );
        object::transfer(coin_info_obj, @coins);
        let coin_store = coin_store::create_coin_store_extend<PRC>();
        let treasury_obj = object::new_named_object(Treasury { coin_store });
        object::transfer_extend(treasury_obj, @coins);
    }

    /// Provide a faucet to give out coins to users
    /// In a real world scenario, the coins should be given out in the application business logic.
    public entry fun faucet(account: &signer) {
        let account_addr = signer::address_of(account);
        let coin_signer = signer::module_signer<Treasury>();
        let coin_info_obj = object::borrow_mut_object<CoinInfo<PRC>>(&coin_signer, coin::coin_info_id<PRC>());
        let coin = coin::mint_extend<PRC>(coin_info_obj, 10000);
        account_coin_store::deposit_extend(account_addr, coin);
    }

    /// This function shows how to use `coin::transfer_extend` to define a custom transfer logic
    /// This transfer function limits the amount of transfer to 10000, and take 1% of the amount as fee
    public entry fun transfer(from: &signer, to_addr: address, amount: u256) {
        assert!(amount <= 10000u256, ErrorTransferAmountTooLarge);
        let from_addr = signer::address_of(from);
        let fee_amount = amount / 100u256;
        if (fee_amount > 0u256) {
            let fee = account_coin_store::withdraw_extend<PRC>(from_addr, fee_amount);
            deposit_to_treaury(fee);
        };
        account_coin_store::transfer_extend<PRC>(from_addr, to_addr, amount);
    }

    fun deposit_to_treaury(coin: Coin<PRC>) {
        let treasury_object_id = object::named_object_id<Treasury>();
        let treasury_obj = object::borrow_mut_object_extend<Treasury>(treasury_object_id);
        coin_store::deposit_extend(&mut object::borrow_mut(treasury_obj).coin_store, coin);
    }
}

Likewise, the type of token and its treasury are defined through two structures. PRC is a private type of token.

Use the private type CoinType to create a token, which allows developers to customize the logic of transfer, withdrawal, and deposit, such as how to customize the transfer fee as demonstrated in the example.

Private type tokens cannot use the general transfer, withdrawl, deposit functions provided in the account_coin_store module.

init defines the minting logic for creating PRC tokens.

The same is done to register the token information CoinInfo and transfer its object to the address where the token contract is issued.
After using create_coin_store_extend to create the CoinStore object, store it in the treasury. Because this is a private Coin, you need to use the extend function with private generics to ensure that it can only be created by the module of CoinType.
Finally, the treasury object is transferred to the address where the token is issued.

Define the faucet function to mint tokens and transfer them to the account.

The transfer function shows how to use coin::transfer_extend to define custom transfer logic. This transfer function limits the transfer amount to 10000 and charges a gas fee of 1% of the amount.

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