Events write logs to the blockchain. They are commonly used by applications to monitor blockchain state and as a cheaper alternative to store data on the blockchain without using state variables.
Events can be efficiently searched by indexing their arguments. Up to 3 parameters can be indexed.
# pragma version ^0.4.0
# up to 3 index
event Transfer:
# enables quick search of all Transfer events where sender is a certain address
sender: indexed(address)
# enables quick search of all Transfer events where receiver is a certain address
receiver: indexed(address)
amount: uint256
@external
def transfer(receiver: address, amount: uint256):
# some code ...
log Transfer(msg.sender, receiver, amount)
@external
def mint(amount: uint256):
# some code ...
log Transfer(empty(address), msg.sender, amount)
@external
def burn(amount: uint256):
# some code ...
log Transfer(msg.sender, empty(address), amount)
