Skip to main content
Version: 5.x

primitive_topic

What it does​

Checks for ink! contracts that use the #[ink(topic)] annotation with primitive number types. Topics are discrete events for which it makes sense to filter. Typical examples of fields that should be filtered are AccountId, bool or enum variants.

Why is this bad?​

It typically doesn't make sense to annotate types like u32 or i32 as a topic, if those fields can take continuous values that could be anywhere between ::MIN and ::MAX. An example of a case where it doesn't make sense at all to have a topic on the storage field is something like value: Balance in the examle below.

Example​

// Bad
// It typically makes no sense to filter `Balance`, since its value may varies from `::MAX`
// to `::MIN`.
#[ink(event)]
pub struct Transaction {
    #[ink(topic)]
    src: Option<AccountId>,
    #[ink(topic)]
    dst: Option<AccountId>,
    #[ink(topic)]
    value: Balance,
}

Use instead:

// Good
// Filtering transactions based on source and destination addresses.
#[ink(event)]
pub struct Transaction {
    #[ink(topic)]
    src: Option<AccountId>,
    #[ink(topic)]
    dst: Option<AccountId>,
    value: Balance,
}