扩展功能

什么是代币扩展功能？

Token Extensions Program（Token 2022）通过称为扩展的额外指令提供更多功能。扩展是您可以为代币 mint 或代币账户添加的可选功能。您可以在 Token Extensions Program 的源代码中找到这些扩展指令的实现。

每个扩展都会添加特定的状态，通常在创建 mint 或代币账户时初始化。在初始化任一账户时，您可以同时启用特定扩展以实现不同的功能。大多数扩展在账户初始化后无法添加。这是设计代币时需要考虑的重要因素，因为您需要提前规划希望代币支持哪些功能。每个扩展的集成指南可在 Token Extensions 开发者文档中找到。

某些扩展彼此不兼容，您无法在同一个代币 mint 或代币账户上同时启用它们。例如，您无法将 NonTransferable 扩展与 TransferFeeConfig 扩展结合使用，因为它们的行为存在冲突。

Token Extensions Program 定义了一个 ExtensionType enum，列出了您可以为代币 mint 或代币账户添加的所有可用扩展。每个变体代表一个具有独特功能的不同扩展。

ExtensionType enum 定义如下：

Token Extensions

/// Extensions that can be applied to mints or accounts.  Mint extensions must
/// only be applied to mint accounts, and account extensions must only be
/// applied to token holding accounts.
#[repr(u16)]
#[cfg_attr(feature = "serde-traits", derive(Serialize, Deserialize))]
#[cfg_attr(feature = "serde-traits", serde(rename_all = "camelCase"))]
#[derive(Clone, Copy, Debug, PartialEq, TryFromPrimitive, IntoPrimitive)]
pub enum ExtensionType {
    /// Used as padding if the account size would otherwise be 355, same as a
    /// multisig
    Uninitialized,
    /// Includes transfer fee rate info and accompanying authorities to withdraw
    /// and set the fee
    TransferFeeConfig,
    /// Includes withheld transfer fees
    TransferFeeAmount,
    /// Includes an optional mint close authority
    MintCloseAuthority,
    /// Auditor configuration for confidential transfers
    ConfidentialTransferMint,
    /// State for confidential transfers
    ConfidentialTransferAccount,
    /// Specifies the default Account::state for new Accounts
    DefaultAccountState,
    /// Indicates that the Account owner authority cannot be changed
    ImmutableOwner,
    /// Require inbound transfers to have memo
    MemoTransfer,
    /// Indicates that the tokens from this mint can't be transferred
    NonTransferable,
    /// Tokens accrue interest over time,
    InterestBearingConfig,
    /// Locks privileged token operations from happening via CPI
    CpiGuard,
    /// Includes an optional permanent delegate
    PermanentDelegate,
    /// Indicates that the tokens in this account belong to a non-transferable
    /// mint
    NonTransferableAccount,
    /// Mint requires a CPI to a program implementing the "transfer hook"
    /// interface
    TransferHook,
    /// Indicates that the tokens in this account belong to a mint with a
    /// transfer hook
    TransferHookAccount,
    /// Includes encrypted withheld fees and the encryption public that they are
    /// encrypted under
    ConfidentialTransferFeeConfig,
    /// Includes confidential withheld transfer fees
    ConfidentialTransferFeeAmount,
    /// Mint contains a pointer to another account (or the same account) that
    /// holds metadata
    MetadataPointer,
    /// Mint contains token-metadata
    TokenMetadata,
    /// Mint contains a pointer to another account (or the same account) that
    /// holds group configurations
    GroupPointer,
    /// Mint contains token group configurations
    TokenGroup,
    /// Mint contains a pointer to another account (or the same account) that
    /// holds group member configurations
    GroupMemberPointer,
    /// Mint contains token group member configurations
    TokenGroupMember,
    /// Mint allowing the minting and burning of confidential tokens
    ConfidentialMintBurn,
    /// Tokens whose UI amount is scaled by a given amount
    ScaledUiAmount,
    /// Tokens where minting / burning / transferring can be paused
    Pausable,
    /// Indicates that the account belongs to a pausable mint
    PausableAccount,

    /// Test variable-length mint extension
    #[cfg(test)]
    VariableLenMintTest = u16::MAX - 2,
    /// Padding extension used to make an account exactly Multisig::LEN, used
    /// for testing
    #[cfg(test)]
    AccountPaddingTest,
    /// Padding extension used to make a mint exactly Multisig::LEN, used for
    /// testing
    #[cfg(test)]
    MintPaddingTest,
}

每个扩展通过向 mint 或代币账户添加额外状态来提供专门的功能。所有扩展特定的状态都存储在 tlv_data 字段中，该字段遵循基本账户数据类型。您必须根据为该账户启用的特定扩展类型进一步反序列化 tlv_data（包含扩展状态）。

Token Extensions

/// Encapsulates immutable base state data (mint or account) with possible
/// extensions, where the base state is Pod for zero-copy serde.
#[derive(Debug, PartialEq)]
pub struct PodStateWithExtensions<'data, S: BaseState + Pod> {
    /// Unpacked base data
    pub base: &'data S,
    /// Slice of data containing all TLV data, deserialized on demand
    tlv_data: &'data [u8],
}

什么是代币扩展功能？

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