This article analyzes the three core components of Sui Move tokens: balance (value storage layer), coin (token operation layer), and pay (payment abstraction layer). Through principle diagrams and code examples, the design principles of the three-layer architecture are revealed.

Modules	Tiers	Function	Scenario
sui::balance	Value storage layer (underlying storage)	Manage the mapping relationship between addresses and token balances	Balance query, token ownership verification
sui::coin	Token operation layer (basic operation)	Focus on the life cycle management of the token itself; including: token creation, destruction and metadata management, etc.	Custom token issuance and token metadata maintenance
sui::pay	Payment abstraction layer (high-level encapsulation)	Provides compound operations for token payment including: single or batch token splitting, merging, transfer, etc.	Batch transfer, split account logic, airdrop

Method diagram

The method is relatively simple, mainly calling cointhe method in balance. The method coinwill be called in, so this article focuses on cointhe core method illustrated.

The principles of regulatory currency will be introduced in a separate article and will be ignored in this article.

Code Examples

module cookbook::aig_token {
    use std::string::{Self, String};
    use std::ascii;
    use sui::coin::{Self, TreasuryCap};
    use sui::balance::{Self, Balance};
    use sui::url::{Self, Url};
    use sui::event;

    public struct EventMint has copy, drop {
        sender: address,
        amount: u64,
        coin_left: u64
    }

    public struct EventAirdrop has copy, drop {
        method: String,
        sender: address,
        amount: u64
    }

    public struct EventCoinMeta has copy, drop {
        decimals: u8,
        symbol: ascii::String,
        name: String,
        description: String,
        icon_url: Option<Url>,
    }

    public struct EventTotalSupply has copy, drop {
        total_supply: u64
    }

    public struct Vault has key {
        id: UID,
        balance: Balance<AIG_TOKEN>,
    }

    public struct AIG_TOKEN has drop {}

    fun init(
        witness: AIG_TOKEN,
        ctx: &mut TxContext
    ) {

        let decimals = 3;
        let symbol = b"AIG";
        let name = b"AIG Token";
        let description = b"AIG Token is a token that is used to incentivize the community to achieve the goals of the AI Goal.";
        let url = url::new_unsafe_from_bytes(b"https://ai-goal.vercel.app/");

        let (treasury_cap, metadata) = coin::create_currency<AIG_TOKEN>(
            witness,
            decimals,
            symbol,
            name,
            description,
            option::some(url),
            ctx
        );

        event::emit(
            EventCoinMeta {
                decimals: coin::get_decimals(&metadata),
                symbol: coin::get_symbol(&metadata),
                name: coin::get_name(&metadata),
                description: coin::get_description(&metadata),
                icon_url: option::some(url),
            }
        );

        transfer::public_freeze_object(metadata);
        transfer::public_transfer(treasury_cap, ctx.sender());

        transfer::share_object(
            Vault {
                id: object::new(ctx),
                balance: balance::zero(),
            }
        );
    }

    public(package) fun airdrop(
        vault: &mut Vault,
        amount: u64,
        method: vector<u8>,
        ctx: &mut TxContext
    ) {
        let sender = ctx.sender();

        let mut balance_drop = balance::split(&mut vault.balance, amount);
        let coin_drop = coin::take(&mut balance_drop, amount, ctx);
        transfer::public_transfer(coin_drop, sender);
        balance::destroy_zero(balance_drop);

        event::emit(
            EventAirdrop {
                method: string::utf8(method),
                sender,
                amount,
            }
        );
    }

    public fun mint_balance(
        treasury_cap: &mut TreasuryCap<AIG_TOKEN>,
        vault: &mut Vault,
        amount: u64,
        ctx: &mut TxContext
    ) {
        let balance_minted = coin::mint_balance(treasury_cap, amount);
        balance::join(&mut vault.balance, balance_minted);

        event::emit(
            EventMint {
                sender: ctx.sender(),
                amount: amount,
                coin_left: balance::value(&vault.balance)
            }
        );
    }

    #[allow(lint(self_transfer))]
    public fun mint_coin(
        treasury_cap: &mut TreasuryCap<AIG_TOKEN>,
        amount: u64,
        ctx: &mut TxContext
    ) {
        let coin_minted = coin::mint(treasury_cap, amount, ctx);
        transfer::public_transfer(coin_minted, ctx.sender());

        coin::mint_and_transfer(
            treasury_cap,
            amount,
            ctx.sender(),
            ctx
        );

        event::emit(
            EventTotalSupply {
                total_supply: coin::total_supply(treasury_cap)
            }
        )
    }
}