alepha@docs:~/docs/reference/primitives$
cat $topic.md | pretty
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#$topic

#Import

typescript 
1import { $topic } from "alepha/topic";

#Overview

Creates a topic primitive for publish/subscribe messaging and event-driven architecture.

Enables decoupled communication through a pub/sub pattern where publishers send messages and multiple subscribers receive them. Supports type-safe messages, real-time delivery, event filtering, and pluggable backends (memory, Redis, custom providers).

Use Cases: User notifications, real-time chat, event broadcasting, microservice communication

#Options

Option Type Required Description
name string No Unique name identifier for the topic
description string No Human-readable description of the topic's purpose and usage
provider "memory" | Service<TopicProvider> No Topic provider configuration for message storage and delivery
schema T Yes Zod schema defining the structure of messages published to this topic
handler TopicHandler<T> No Default subscriber handler function that processes messages published to this topic
retain boolean No Whether the last published message should be retained and delivered to new subscribers

#Examples

ts 
 1class NotificationService { 2  dateTime = $inject(DateTimeProvider); 3  4  userActivity = $topic({ 5    name: "user-activity", 6    schema: { 7      payload: z.object({ 8        userId: z.text(), 9        action: z.enum(["login", "logout", "purchase"]),10        timestamp: z.number()11      })12    },13    handler: async (message) => {14      console.log(`User ${message.payload.userId}: ${message.payload.action}`);15    }16  });17 18  async trackLogin(userId: string) {19    await this.userActivity.publish({ userId, action: "login", timestamp: this.dateTime.nowMillis() });20  }21 22  async subscribeToEvents() {23    await this.userActivity.subscribe(async (message) => {24      // Additional subscriber logic25    });26  }27}