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Version: 3.x.x

#[ink(topic)]

Applied on fields of ink! event types to indicate that they are topics.

Tells the ink! codegen to provide a topic hash for the given field. Every ink! event can only have a limited number of such topic field. The semnatics are similar to indexed event arguments in Solidity.

Example

#[ink(event)]
pub struct Transferred {
#[ink(topic)]
from: Option<AccountId>,

#[ink(topic)]
to: Option<AccountId>,

amount: Balance
}