環境變數與常數

環境變數

Environment variables always exist in the namespace and are primarily used to provide information about the blockchain or current transaction.

區塊與交易屬性

Name	Type	Value
block.coinbase	address	Current block miner’s address
block.difficulty	uint256	Current block difficulty
block.prevrandao	bytes32	Current randomness beacon provided by the beacon chain
block.number	uint256	Current block number
block.gaslimit	uint256	Current block’s gas limit
block.basefee	uint256	Current block’s base fee
block.blobbasefee	uint256	Current block’s blob gas base fee
block.prevhash	bytes32	Equivalent to blockhash(block.number - 1)
block.timestamp	uint256	Current block epoch timestamp
chain.id	uint256	Chain ID
msg.data	Bytes	訊息資料
msg.gas	uint256	Remaining gas
msg.mana	uint256	Remaining gas (alias for msg.gas)
msg.sender	address	Sender of the message (current call)
msg.value	uint256	Number of wei sent with the message
tx.origin	address	Sender of the transaction (full call chain)
tx.gasprice	uint256	Gas price of current transaction in wei

備註

block.prevrandao is an alias for the block.difficulty opcode. Since block.difficulty is considered deprecated according to EIP-4399 after 「The Merge」 (Paris hard fork), we recommend using block.prevrandao.

備註

msg.data requires the usage of slice to explicitly extract a section of calldata. If the extracted section exceeds the bounds of calldata, this will throw. You can check the size of msg.data using len.

The self Variable

self is an environment variable used to reference a contract from within itself. Along with the normal address members, self allows you to read and write to state variables and to call internal functions within the contract.

Name	Type	Value
self	address	Current contract’s address
self.balance	uint256	Current contract’s balance

Accessing State Variables

self is used to access a contract’s state variables, as shown in the following example:

state_var: uint256

@external
def set_var(value: uint256) -> bool:
    self.state_var = value
    return True

@external
@view
def get_var() -> uint256:
    return self.state_var

Calling Internal Functions

self is also used to call internal functions within a contract:

@internal
def _times_two(amount: uint256) -> uint256:
    return amount * 2

@external
def calculate(amount: uint256) -> uint256:
    return self._times_two(amount)

Custom Constants

Custom constants can be defined at a global level in Vyper. To define a constant, make use of the constant keyword.

TOTAL_SUPPLY: constant(uint256) = 10000000
total_supply: public(uint256)

@deploy
def __init__():
    self.total_supply = TOTAL_SUPPLY