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x/evt/lib/util/genericOperators/distinct.ts

💧EventEmitter's typesafe replacement
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import { compose } from "../compose.ts";
type CtxLike = { evtDoneOrAborted: { postCount: number; } };
export const distinct = <T>( keySelector?: ((value: T) => any) | undefined, ctxFlush?: CtxLike) => compose< T, { data: T, selectedKey: any, currentFlushCount: number; }, { boxedData: [T] | null; alreadyPostedData: Set<any>; previousFlushCount: number }, T>( data => [{ data, "selectedKey": keySelector?.(data) ?? data, "currentFlushCount": ctxFlush?.evtDoneOrAborted.postCount ?? 0 }], [ ({ data, selectedKey, currentFlushCount }, { alreadyPostedData, previousFlushCount }) => [{ "boxedData": ( currentFlushCount !== previousFlushCount || !alreadyPostedData.has(selectedKey) ) ? [data] : null, "alreadyPostedData": new Set([ ...( currentFlushCount !== previousFlushCount ? [] : Array.from(alreadyPostedData) ), selectedKey ]), "previousFlushCount": currentFlushCount }], { "boxedData": null, "alreadyPostedData": new Set(), "previousFlushCount": ctxFlush?.evtDoneOrAborted.postCount ?? 0 } ], ({ boxedData }) => boxedData);