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# Advanced Operations
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Advanced features including low-level dispatch operations, pass-by-copy semantics, timing estimates, and specialized promise operations.
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## Capabilities
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### Low-Level Dispatch Operations
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Generic operation dispatch system for advanced promise manipulation.
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```javascript { .api }
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/**
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 * Generic operation dispatch on fulfilled value
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 * @param op - Operation name to dispatch
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 * @param args - Arguments for the operation
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 * @returns Promise for operation result
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 */
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promise.dispatch(op, args);
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/**
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 * Low-level dispatch without promise wrapping
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 * @param resolve - Resolver function for the result
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 * @param op - Operation name to dispatch
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 * @param args - Arguments for the operation
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 * @returns void (calls resolve with result)
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 */
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promise.rawDispatch(resolve, op, args);
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/**
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 * Generic operation dispatch on values (deprecated)
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 * @param value - Value to operate on
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 * @param op - Operation name
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 * @param operands - Operation arguments
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 * @returns Promise for operation result
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 */
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function Q.dispatch(value, op, operands);
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```
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**Usage Examples:**
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```javascript
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const Q = require("q");
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// Custom dispatch operations
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const objectPromise = Q.resolve({
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  values: [1, 2, 3, 4, 5],
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  transform: function(fn) { return this.values.map(fn); },
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  sum: function() { return this.values.reduce((a, b) => a + b, 0); }
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});
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// Dispatch custom operations
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objectPromise.dispatch("transform", [x => x * 2])
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  .then(doubled => console.log("Doubled:", doubled)); // [2, 4, 6, 8, 10]
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objectPromise.dispatch("sum", [])
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  .then(sum => console.log("Sum:", sum)); // 15
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// Raw dispatch for performance-critical operations
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function performRawOperation(promise, operation, args) {
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  return new Q.Promise((resolve, reject) => {
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    promise.rawDispatch((result) => {
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      try {
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        const operationResult = result[operation].apply(result, args);
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        resolve(operationResult);
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      } catch (error) {
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        reject(error);
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      }
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    }, operation, args);
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  });
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}
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// Using Q.dispatch (deprecated but still functional)
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Q.dispatch({ name: "John" }, "get", ["name"])
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  .then(name => console.log("Name:", name));
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// Advanced dispatch patterns
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class PromiseDispatcher {
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  constructor(promise) {
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    this.promise = promise;
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  }
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  dispatchOperation(op, ...args) {
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    return this.promise.dispatch(op, args);
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  }
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  dispatchMultiple(operations) {
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    const dispatches = operations.map(({ op, args }) => 
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      this.promise.dispatch(op, args)
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    );
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    return Q.all(dispatches);
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  }
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}
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// Usage
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const dispatcher = new PromiseDispatcher(objectPromise);
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dispatcher.dispatchMultiple([
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  { op: "sum", args: [] },
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  { op: "transform", args: [x => x + 1] }
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]).then(results => {
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  console.log("Dispatch results:", results);
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});
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```
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### Pass-by-Copy Semantics
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System for marking values and promises for pass-by-copy serialization behavior.
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```javascript { .api }
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/**
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 * Marks value for pass-by-copy semantics
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 * @param value - Value to mark for pass-by-copy
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 * @returns Value marked for pass-by-copy
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 */
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function Q.passByCopy(value);
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// Alias: Q.push(value)
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/**
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 * Checks if value is marked for pass-by-copy
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 * @param value - Value to check
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 * @returns True if value is marked for pass-by-copy
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 */
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function Q.isPortable(value);
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/**
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 * Marks promise for pass-by-copy semantics
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 * @returns Promise marked for pass-by-copy
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 */
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promise.pass();
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/**
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 * Checks if promise is marked for pass-by-copy
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 * @returns True if promise is marked for pass-by-copy
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 */
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promise.toBePassed();
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/**
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 * Creates pass-by-copy snapshot of fulfilled object
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 * @returns Promise for serializable snapshot
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 */
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promise.pull();
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```
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**Usage Examples:**
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```javascript
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const Q = require("q");
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// Mark values for pass-by-copy
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const portableData = Q.passByCopy({
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  name: "John",
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  age: 30,
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  preferences: { theme: "dark" }
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});
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console.log(Q.isPortable(portableData)); // true
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// Mark promises for pass-by-copy
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const userPromise = fetchUser(123).pass();
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console.log(userPromise.toBePassed()); // true
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// Create serializable snapshots
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const complexObjectPromise = Q.resolve({
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  id: 1,
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  data: new Map([["key1", "value1"], ["key2", "value2"]]),
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  timestamp: new Date(),
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  process: () => "cannot be serialized"
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});
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complexObjectPromise.pull()
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  .then(snapshot => {
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    console.log("Serializable snapshot:", snapshot);
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    // Contains only serializable properties
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  });
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// Distributed computing example
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function createDistributableTask(data) {
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  const portableData = Q.passByCopy(data);
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  return Q.resolve(portableData)
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    .pass() // Mark promise as portable
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    .then(data => {
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      // This promise can be serialized and sent to remote workers
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      return processOnRemoteWorker(data);
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    });
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}
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// Serialization utility
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function serializePromiseChain(promise) {
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  if (promise.toBePassed()) {
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    return promise.pull().then(data => ({
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      type: "serialized_promise",
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      data: JSON.stringify(data),
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      portable: true
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    }));
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  } else {
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    throw new Error("Promise is not marked for serialization");
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  }
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}
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// Remote execution pattern
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function executeRemoteley(localPromise) {
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  return localPromise
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    .pass()
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    .pull()
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    .then(serializableData => {
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      return sendToRemoteWorker(serializableData);
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    })
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    .then(remoteResult => {
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      return Q.passByCopy(remoteResult);
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    });
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}
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```
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### Timing Estimates
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System for tracking and observing promise completion time estimates.
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```javascript { .api }
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/**
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 * Observes changes to completion time estimates
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 * @param emit - Callback for estimate changes
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 * @returns Promise with estimate observation
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 */
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promise.observeEstimate(emit);
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/**
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 * Gets current completion time estimate
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 * @returns Current estimate in milliseconds
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 */
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promise.getEstimate();
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/**
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 * Sets completion time estimate on deferred
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 * @param estimate - Estimate in milliseconds
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 * @returns void
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 */
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deferred.setEstimate(estimate);
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```
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**Usage Examples:**
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```javascript
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const Q = require("q");
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// Set estimates on deferred objects
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const deferred = Q.defer();
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deferred.setEstimate(5000); // Estimate 5 seconds
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// Monitor estimate changes
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deferred.promise.observeEstimate((estimate) => {
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  console.log(`Estimated completion in: ${estimate}ms`);
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});
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// Simulate work with estimate updates
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setTimeout(() => {
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  deferred.setEstimate(3000); // Update to 3 seconds
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}, 1000);
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setTimeout(() => {
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  deferred.setEstimate(1000); // Update to 1 second
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}, 2000);
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setTimeout(() => {
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  deferred.resolve("Task completed");
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}, 3000);
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// Get current estimates
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console.log("Initial estimate:", deferred.promise.getEstimate());
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// Progress tracking utility
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class ProgressTracker {
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  constructor(promise, name) {
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    this.promise = promise;
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    this.name = name;
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    this.startTime = Date.now();
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    this.setupEstimateObserver();
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  }
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  setupEstimateObserver() {
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    this.promise.observeEstimate((estimate) => {
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      const elapsed = Date.now() - this.startTime;
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      const remaining = Math.max(0, estimate - elapsed);
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      console.log(`${this.name}: ${remaining}ms remaining (${elapsed}ms elapsed)`);
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      if (remaining > 0) {
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        const percentage = (elapsed / estimate) * 100;
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        this.updateProgressBar(Math.min(100, percentage));
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      }
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    });
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  }
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  updateProgressBar(percentage) {
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    const bar = "█".repeat(Math.floor(percentage / 5)) + 
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                "░".repeat(20 - Math.floor(percentage / 5));
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    console.log(`${this.name}: [${bar}] ${percentage.toFixed(1)}%`);
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  }
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}
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// Usage
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function longRunningTask() {
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  const deferred = Q.defer();
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  deferred.setEstimate(10000); // 10 seconds
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  let progress = 0;
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  const timer = setInterval(() => {
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    progress += 1000;
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    deferred.setEstimate(10000 - progress);
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    if (progress >= 10000) {
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      clearInterval(timer);
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      deferred.resolve("Task completed");
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    }
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  }, 1000);
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  return deferred.promise;
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}
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const tracker = new ProgressTracker(longRunningTask(), "Data Processing");
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```
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### Iterator Support
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Support for creating iterators from promised iterable values.
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```javascript { .api }
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/**
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 * Creates iterator for fulfilled iterable value
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 * @returns Promise for iterator object
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 */
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promise.iterate();
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```
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**Usage Examples:**
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```javascript
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const Q = require("q");
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// Create iterator from promised array
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const arrayPromise = Q.resolve([1, 2, 3, 4, 5]);
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arrayPromise.iterate()
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  .then(iterator => {
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    console.log(iterator.next()); // { value: 1, done: false }
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    console.log(iterator.next()); // { value: 2, done: false }
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    console.log(iterator.next()); // { value: 3, done: false }
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  });
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// Async iteration utility
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function asyncIterate(iterablePromise, processor) {
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  return iterablePromise.iterate().then(iterator => {
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    const results = [];
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    function processNext() {
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      const { value, done } = iterator.next();
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      if (done) {
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        return results;
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      }
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      return Q.resolve(processor(value))
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        .then(processedValue => {
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          results.push(processedValue);
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          return processNext();
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        });
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    }
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    return processNext();
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  });
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}
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// Usage
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const numbersPromise = Q.resolve([1, 2, 3, 4, 5]);
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asyncIterate(numbersPromise, num => Q.delay(num * 2, 100))
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  .then(results => console.log("Processed results:", results));
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// Stream processing with iterators
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function streamProcess(dataPromise, batchSize = 3) {
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  return dataPromise.iterate().then(iterator => {
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    const batches = [];
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    let currentBatch = [];
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    function processBatch() {
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      const { value, done } = iterator.next();
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      if (done) {
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        if (currentBatch.length > 0) {
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          batches.push(currentBatch);
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        }
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        return batches;
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      }
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      currentBatch.push(value);
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      if (currentBatch.length >= batchSize) {
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        batches.push(currentBatch);
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        currentBatch = [];
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      }
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      return processBatch();
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    }
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    return processBatch();
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  });
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}
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// Usage
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const largeDatasetPromise = Q.resolve(Array.from({ length: 10 }, (_, i) => i + 1));
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streamProcess(largeDatasetPromise, 3)
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  .then(batches => {
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    console.log("Processed in batches:", batches);
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    // [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10]]
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  });
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```