solana-sysvar 0.0.2

Access to special accounts with dynamically-updated data. Sysvars are special accounts that contain dynamically-updated data about the network cluster, the blockchain history, and the executing transaction. Each sysvar is defined in its own submodule within this module. The [`clock`], [`epoch_schedule`], [`instructions`], and [`rent`] sysvars are most useful to on-chain programs. Simple sysvars implement the [`Sysvar::get`] method, which loads a sysvar directly from the runtime, as in this example that logs the `clock` sysvar: ``` use solana_account_info::AccountInfo; use solana_msg::msg; use solana_sysvar::Sysvar; use solana_program_error::ProgramResult; use solana_pubkey::Pubkey; fn process_instruction( program_id: &Pubkey, accounts: &[AccountInfo], instruction_data: &[u8], ) -> ProgramResult { let clock = solana_clock::Clock::get()?; msg!("clock: {:#?}", clock); Ok(()) } ``` Since Solana sysvars are accounts, if the `AccountInfo` is provided to the program, then the program can deserialize the sysvar with [`Sysvar::from_account_info`] to access its data, as in this example that again logs the [`clock`] sysvar. ``` use solana_account_info::{AccountInfo, next_account_info}; use solana_msg::msg; use solana_sysvar::Sysvar; use solana_program_error::ProgramResult; use solana_pubkey::Pubkey; fn process_instruction( program_id: &Pubkey, accounts: &[AccountInfo], instruction_data: &[u8], ) -> ProgramResult { let account_info_iter = &mut accounts.iter(); let clock_account = next_account_info(account_info_iter)?; let clock = solana_clock::Clock::from_account_info(&clock_account)?; msg!("clock: {:#?}", clock); Ok(()) } ``` When possible, programs should prefer to call `Sysvar::get` instead of deserializing with `Sysvar::from_account_info`, as the latter imposes extra overhead of deserialization while also requiring the sysvar account address be passed to the program, wasting the limited space available to transactions. Deserializing sysvars that can instead be retrieved with `Sysvar::get` should be only be considered for compatibility with older programs that pass around sysvar accounts. Some sysvars are too large to deserialize within a program, and `Sysvar::from_account_info` returns an error, or the serialization attempt will exhaust the program's compute budget. Some sysvars do not implement `Sysvar::get` and return an error. Some sysvars have custom deserializers that do not implement the `Sysvar` trait. These cases are documented in the modules for individual sysvars. All sysvar accounts are owned by the account identified by [`sysvar::ID`]. [`sysvar::ID`]: https://docs.rs/solana-sdk-ids/latest/solana_sdk_ids/sysvar/constant.ID.html For more details see the Solana [documentation on sysvars][sysvardoc]. [sysvardoc]: https://docs.solanalabs.com/runtime/sysvars