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Core Concepts
Coin

Coin and Fungible Token

In Rooch, Coin is a concrete implementation of Fungible Token. It is included in the coin module (opens in a new tab) of the RoochFramework.

Coin Type

struct Coin<phantom CoinType : key> {
    value: u256,
}

Coin is a generic type that contains a value field representing the value of the Coin. The type parameter CoinType of Coin represents the type of the Coin. In Rooch, the unique identifier for an asset type is CoinType, not the contract address, which is different from the ERC20 standard.

For example, the type of Gas Coin in Rooch is 0x3::gas_coin::RGas. Here, 0x3 is the contract address of RoochFramework, gas_coin is the module name, and RGas is the type name. These three together form a unique type identifier.

Registering Coin Type

First, developers need to define a custom CoinType, then use the coin::register_extend function to create a CoinInfo object. The CoinInfo object stores relevant information about the Coin type, such as name, symbol, icon, decimals, etc. It also represents the management authority of the Coin.

    #[private_generics(CoinType)]
    public fun register_extend<CoinType: key>(
        name: string::String,
        symbol: string::String,
        icon_url: Option<string::String>,
        decimals: u8,
    ): Object<CoinInfo<CoinType>>

Note that this function is protected by private_generics and can only be called within the CoinType module.

CoinStore

The Coin type doesn't have any ability, so it can't be stored directly in structures. It needs to be stored through CoinStore. By default, the system creates a CoinStore for each address of each CoinType. Developers can also use the coin::create_coin_store function to create Object<CoinStore<CoinType>>. CoinStore objects can be stored in any structure.

    public fun create_coin_store<CoinType: key + store>(): Object<CoinStore<CoinType>>

Private Coin and Public Coin

In Rooch, if CoinType doesn't have the store ability, then the Coin is a Private Coin, otherwise it's a Public Coin.

  • Private Coin can only be transferred within the CoinType module and cannot be transferred outside the module.
  • Public Coin can be transferred by any module. Users can directly call the transfer::transfer_coin function to transfer Public Coin.

If developers need to customize the transfer logic of Coin, they can implement it by calling the coin::transfer_extend function within their own module.

Note that all functions with the extend keyword in coin and coin_store are protected by private_generics, indicating that these functions are for CoinType module developers to extend.

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This section is still being improved! More explanations about Coin methods need to be added:

  • mint and burn methods.
  • coin_store related methods.
  • account_coin_store related methods.

Coins Examples

Storage abstractionRGas