> For the complete documentation index, see [llms.txt](https://docs.xy.finance/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.xy.finance/single-bridge-integration/xasset-bridge/how-to-develop-under-xy-standards/function-interface-for-token-contract.md).

# Function Interface for Token Contract

### Function: mint

Your contract should include the `mint` function. Here is the signature:

```solidity
function mint(
    address to,
    uint256 amount
) external onlyMinter;
```

This function creates new tokens and adds them to the total supply. The parameters are:

* `address to`: The address to receive the newly minted tokens.
* `uint256 amount`: The amount of tokens to be minted and sent to the designated address.

Here is a brief implementation example of the `mint` function using OpenZeppelin's ERC20 library:

```solidity
// Using OpenZeppelin's ERC20
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract MyToken is ERC20 {
    // ...
    function mint(address to, uint256 amount) public onlyMinter {
        _mint(to, amount);
    }
}
```

The `onlyMinter` modifier restricts access to the `mint` function to authorized minters only, ensuring control over the creation of new tokens.

This `mint` function is key to the effective operation of cross-chain transfers within our system. By minting tokens on the destination chain that correspond tokens burnt on the source chain, the `mint` function ensures that total token supply remains consistent across all chains

### Accessing the Minter Role

In order to use the `mint` function, you will need to provide **our relay contract** with permission to pass the `onlyMinter` check. This necessitates the inclusion of a function in your contract that enables the assignment of the minter role.

Possible options are:

1. **Mapping for Minters**: Use a mapping in your contract to track the minter access of addresses. 
2. **Grant Role Function**: Use a function in your contract that allows a specific role, such as an owner or admin, to grant the minter role. This can be done using a role-based access control library like OpenZeppelin's Access Control library.

### Function: burn

Your contract should also implement a `burn` function for token destruction. We expect this function will burn/remove a certain amount of tokens. We currently support the two interfaces for burn function:

#### XYERC20 (V1)

```solidity
function burn(
    uint256 amount
) external;
```

This `burn` function should destroy a specified amount of tokens from the `msg.sender`'s balance. The parameter is:

* `uint256 amount`: The number of tokens to be burnt or destroyed.

Here is a brief implementation of the `burn` function using OpenZeppelin's ERC20 library:

```solidity
// Using OpenZeppelin's ERC20
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract MyToken is ERC20 {
    // ...
    function burn(uint256 amount) external {
        _burn(msg.sender, amount);
    }
}
```

In this example, the `_burn` function, a part of OpenZeppelin's ERC20 library, is used to burn tokens. It deducts the `amount` from `msg.sender`'s balance and reduces the total supply of tokens accordingly.

#### XYERC20 (V2)

```solidity
function burn(
    address account,
    uint256 amount
) external onlyMinter;
```

This `burn` function should destroy a specified amount of tokens from the `account`'s balance. The parameters are:

* `address account`: The address of the account from which the tokens will be burned.
* `uint256 amount`: The number of tokens to be burnt or destroyed.

Make sure you add the `onlyMinter` modifier or such access control function to protect this burn function, and you will need to provide **our relay contract** with permission to pass the `onlyMinter` check as well.

***

The `burn` function empowers your contract to maintain the integrity of the token's supply when tokens are sent across different blockchains.


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