prefer-map-entry

Prefer one map entry operation over a guarded insertion

Checking a map before inserting a missing value performs the same key lookup twice.
Instead, you SHOULD use getOrInsertWith to combine the lookup and conditional insertion.

- Category: performance
- Level: warning
- Fix: suggestion
- Scope: module

Reported

import { Map } from "destack:collections";

function ensureValue(values: Map<string, int32>, key: string): void {
    if (!values.has(key)) {
        values.set(key, 1);
    }
}
Accepted

import { Map } from "destack:collections";

function ensureValue(values: Map<string, int32>, key: string): void {
    values.getOrInsertWith(key, () => 1);
}
Prior art

- Clippy · mapentry

language/linter/src/rules/performance/prefermapentry.rs:8