ERC20Drop

/**
*  @notice          Lets an owner a given amount of their tokens.
*  @dev             Caller should own the `_amount` of tokens.
*
*  @param _amount   The number of tokens to burn.
*/
function burn(uint256 _amount) external virtual {
    require(balanceOf(msg.sender) >= _amount, "not enough balance");
    _burn(msg.sender, _amount);
}

/// @dev Collects and distributes the primary sale value of tokens being claimed.
function _collectPriceOnClaim(
    address _primarySaleRecipient,
    uint256 _quantityToClaim,
    address _currency,
    uint256 _pricePerToken
) internal virtual override {
    if (_pricePerToken == 0) {
        return;
    }
 
    uint256 totalPrice = (_quantityToClaim * _pricePerToken) / 1 ether;
    require(totalPrice > 0, "quantity too low");
 
    if (_currency == CurrencyTransferLib.NATIVE_TOKEN) {
        require(msg.value == totalPrice, "Must send total price.");
    }
 
    address saleRecipient = _primarySaleRecipient == address(0) ? primarySaleRecipient() : _primarySaleRecipient;
    CurrencyTransferLib.transferCurrency(_currency, msg.sender, saleRecipient, totalPrice);
}

/// @dev Transfers the tokens being claimed.
function _transferTokensOnClaim(address _to, uint256 _quantityBeingClaimed)
    internal
    virtual
    override
    returns (uint256)
{
    _mint(_to, _quantityBeingClaimed);
    return 0;
}