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‎README.md

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[![Continuous Integration](https://github.com/kaiosilveira/replace-constructor-with-factory-function-refactoring/actions/workflows/ci.yml/badge.svg)](https://github.com/kaiosilveira/replace-constructor-with-factory-function-refactoring/actions/workflows/ci.yml)
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# Refactoring catalog repository template
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This is a quick template to help me get a new refactoring repo going.
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## Things to do after creating a repo off of this template
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1. Run `GITHUB_TOKEN=$(gh auth token) yarn tools:cli prepare-repository -r <repo_name>`. It will:
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- Update the `README.md` file with the actual repository name, CI badge, and commit history link
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- Update `package.json` with the repository's name and remote URL
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- Update the repo's homepage on GitHub with:
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- A description
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- A website link to https://github.com/kaiosilveira/refactoring
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- The following labels: javascript, refactoring, replace-constructor-with-factory-function-refactoring
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2. Replace the lorem ipsum text sections below with actual text
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## Useful commands
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- Generate markdown containing a diff with patch information based on a range of commits:
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```bash
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yarn tools:cli generate-diff -f <first_commit_sha> -l <last_commit_sha>
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```
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- To generate the commit history table for the last section, including the correct links:
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```bash
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yarn tools:cli generate-cmt-table -r replace-constructor-with-factory-function-refactoring
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```
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---
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ℹ️ _This repository is part of my Refactoring catalog based on Fowler's book with the same title. Please see [kaiosilveira/refactoring](https://github.com/kaiosilveira/refactoring) for more details._
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---
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# Replace Constructor With Factory Function
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**Formerly: Old name**
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**Formerly: Replace Constructor with Factory Method**
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<table>
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<thead>
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<td>
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```javascript
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result = initial.code;
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leadEngineer = new Employee(document.leadEngineer, 'E');
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```
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</td>
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<td>
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```javascript
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result = newCode();
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function newCode() {
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return 'new code';
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}
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leadEngineer = createEngineer(document.leadEngineer);
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```
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</td>
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</tr>
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</tbody>
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</table>
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**Inverse of: [Another refactoring](https://github.com/kaiosilveira/refactoring)**
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**Refactoring introduction and motivation** dolore sunt deserunt proident enim excepteur et cillum duis velit dolor. Aute proident laborum officia velit culpa enim occaecat officia sunt aute labore id anim minim. Eu minim esse eiusmod enim nulla Lorem. Enim velit in minim anim anim ad duis aute ipsum voluptate do nulla. Ad tempor sint dolore et ullamco aute nulla irure sunt commodo nulla aliquip.
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Sometimes we need more control over initialization than a constructor can possibly provide, and that's where a [Factory Method](https://github.com/kaiosilveira/design-patterns/tree/main/factory-method) comes in handy: it can hide complex initialization logic, replace the resulting instance with a proxy or decorate it with complementary behavior. This refactoring helps with moving towards this approach.
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## Working example
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**Working example general explanation** proident reprehenderit mollit non voluptate ea aliquip ad ipsum anim veniam non nostrud. Cupidatat labore occaecat labore veniam incididunt pariatur elit officia. Aute nisi in nulla non dolor ullamco ut dolore do irure sit nulla incididunt enim. Cupidatat aliquip minim culpa enim. Fugiat occaecat qui nostrud nostrud eu exercitation Lorem pariatur fugiat ea consectetur pariatur irure. Officia dolore veniam duis duis eu eiusmod cupidatat laboris duis ad proident adipisicing. Minim veniam consectetur ut deserunt fugiat id incididunt reprehenderit.
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Our working example is a program that creates `Employee` instances based on a document input plus employee type. The `Employee` class is straightforward:
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### Test suite
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```javascript
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export class Employee {
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constructor(name, typeCode) {
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this._name = name;
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this._typeCode = typeCode;
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}
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get name() {
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return this._name;
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}
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get type() {
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return Employee.legalTypeCodes[this._typeCode];
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}
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static get legalTypeCodes() {
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return { E: 'Engineer', M: 'Manager', S: 'Salesperson' };
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}
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}
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```
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Occaecat et incididunt aliquip ex id dolore. Et excepteur et ea aute culpa fugiat consectetur veniam aliqua. Adipisicing amet reprehenderit elit qui.
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And some possible usages are:
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```javascript
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describe('functionBeingRefactored', () => {
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it('should work', () => {
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expect(0).toEqual(1);
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});
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});
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const candidateDoc = { name: 'John Doe', empType: 'E' };
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const candidate = new Employee(candidateDoc.name, candidateDoc.empType);
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const leadEngineerDoc = { leadEngineer: 'Jane Doe' };
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const leadEngineer = new Employee(leadEngineerDoc.leadEngineer, 'E');
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console.log(`Candidate: ${candidate.name}, ${candidate.type}`);
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console.log(`Lead engineer: ${leadEngineer.name}, ${leadEngineer.type}`);
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```
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Magna ut tempor et ut elit culpa id minim Lorem aliqua laboris aliqua dolor. Irure mollit ad in et enim consequat cillum voluptate et amet esse. Fugiat incididunt ea nulla cupidatat magna enim adipisicing consequat aliquip commodo elit et. Mollit aute irure consequat sunt. Dolor consequat elit voluptate aute duis qui eu do veniam laborum elit quis.
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Our goal here is to introduce a factory function, so clients don't do `new` employees any longer.
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### Test suite
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Since we're doing with a simple class, there is no test suite in place. Tests will be introduced as we go, though, for the `createEmployee` factory function.
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### Steps
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**Step 1 description** mollit eu nulla mollit irure sint proident sint ipsum deserunt ad consectetur laborum incididunt aliqua. Officia occaecat deserunt in aute veniam sunt ad fugiat culpa sunt velit nulla. Pariatur anim sit minim sit duis mollit.
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We start by introducing the `createEmployee` function:
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```diff
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diff --git top level...
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+export function createEmployee(name, typeCode) {
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+ return new Employee(name, typeCode);
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+}
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```
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Then, we update the callers to use the function instead of initializing the class themselves:
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```diff
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diff --git top level...
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-const candidate = new Employee(candidateDoc.name, candidateDoc.empType);
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+const candidate = createEmployee(candidateDoc.name, candidateDoc.empType);
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// ...
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-const leadEngineer = new Employee(leadEngineerDoc.leadEngineer, 'E');
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+const leadEngineer = createEmployee(leadEngineerDoc.leadEngineer, 'E');
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```
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With that in place, and since we're only creating engineer employees, a decision was made to make the function more specific. We start by renaming `createEmployee` to `createEngineer`:
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```diff
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-const candidate = createEmployee(candidateDoc.name, candidateDoc.empType);
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+const candidate = createEngineer(candidateDoc.name, candidateDoc.empType);
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// ...
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-const leadEngineer = createEmployee(leadEngineerDoc.leadEngineer, 'E');
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+const leadEngineer = createEngineer(leadEngineerDoc.leadEngineer, 'E');
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// ...
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-export function createEmployee(name, typeCode) {
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+export function createEngineer(name, typeCode) {
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```
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And then, we make the employee type fixed to `'E'` at `createEngineer`:
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```diff
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diff --git a/src/price-order/index.js b/src/price-order/index.js
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-module.exports = old;
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+module.exports = new;
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diff --git top level...
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export function createEngineer(name, typeCode) {
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- return new Employee(name, typeCode);
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+ return new Employee(name, 'E');
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```
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**Step n description** mollit eu nulla mollit irure sint proident sint ipsum deserunt ad consectetur laborum incididunt aliqua. Officia occaecat deserunt in aute veniam sunt ad fugiat culpa sunt velit nulla. Pariatur anim sit minim sit duis mollit.
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Finally, we can [remove the flag argument](https://github.com/kaiosilveira/remove-flag-argument-refactoring) `typeCode` from `createEngineer`:
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```diff
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diff --git a/src/price-order/index.js b/src/price-order/index.js
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-module.exports = old;
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+module.exports = new;
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diff --git top level...
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-export function createEngineer(name, typeCode) {
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+export function createEngineer(name) {
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```
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And that's it!
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Below there's the commit history for the steps detailed above.
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| Commit SHA | Message |
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| --------------------------------------------------------------------------- | ------------------------ |
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| [cmt-sha-1](https://github.com/kaiosilveira/replace-constructor-with-factory-function-refactoring/commit-SHA-1) | description of commit #1 |
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| [cmt-sha-2](https://github.com/kaiosilveira/replace-constructor-with-factory-function-refactoring/commit-SHA-2) | description of commit #2 |
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| [cmt-sha-n](https://github.com/kaiosilveira/replace-constructor-with-factory-function-refactoring/commit-SHA-n) | description of commit #n |
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| Commit SHA | Message |
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| ------------------------------------------------------------------------------------------------------------------------------------------------ | ----------------------------------------------------------------------------------- |
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| [3ff0ba7](https://github.com/kaiosilveira/replace-constructor-with-factory-function-refactoring/commit/3ff0ba7a63d438f2c52835038fecbc32abd566dc) | introduce `createEmployee` function |
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| [75b2e05](https://github.com/kaiosilveira/replace-constructor-with-factory-function-refactoring/commit/75b2e05b7bc438e28634607907cea334524c8f13) | update callers to use `createEmployee` instead of initializing the class themselves |
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| [e48639d](https://github.com/kaiosilveira/replace-constructor-with-factory-function-refactoring/commit/e48639dc8b4318c8619e92a7a4d300fe98e9b08b) | rename `createEmployee` to `createEngineer` |
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| [9886939](https://github.com/kaiosilveira/replace-constructor-with-factory-function-refactoring/commit/988693979e648c571d8ed30097df3fe25329fc4a) | make employee type fixed to `'E'` at `createEngineer` |
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| [b15df82](https://github.com/kaiosilveira/replace-constructor-with-factory-function-refactoring/commit/b15df829e562eff6d02e1cc61b36dcf6e66634c4) | remove `typeCode` argument from `createEngineer` |
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For the full commit history for this project, check the [Commit History tab](https://github.com/kaiosilveira/replace-constructor-with-factory-function-refactoring/commits/main).
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For the full commit history for this project, check the [Commit History tab](https://github.com/kaiosilveira/replace-constructor-with-factory-function-refactoring/commits/main).

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