interface IStdReference {
    /// A structure returned whenever someone requests for standard reference data.
    struct ReferenceData {
        uint256 rate; // base/quote exchange rate, multiplied by 1e18.
        uint256 lastUpdatedBase; // UNIX epoch of the last time when base price gets updated.
        uint256 lastUpdatedQuote; // UNIX epoch of the last time when quote price gets updated.
    }

    /// Returns the price data for the given base/quote pair. Revert if not available.
    function getReferenceData(string memory _base, string memory _quote)
        external
        view
        returns (ReferenceData memory);

    /// Similar to getReferenceData, but with multiple base/quote pairs at once.
    function getReferenceDataBulk(string[] memory _bases, string[] memory _quotes)
        external
        view
        returns (ReferenceData[] memory);
}
function getReferenceData(string memory _base, string memory _quote)
    external
    view
    returns (ReferenceData memory);

/// Returns the price data for the given base/quote pair. Revert if not available.