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Compile-time checks for fluent types in TypeScript.
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| export class Person { | |
| private _designation: string; | |
| private _first: string; | |
| private _last: string; | |
| static create(): FluentPerson { | |
| return new Person(); | |
| } | |
| private constructor() { | |
| this._designation = ""; | |
| this._first = ""; | |
| this._last = ""; | |
| } | |
| withDesignation(first: string) { | |
| this._first = first; | |
| return this; | |
| } | |
| withFirst(first: string) { | |
| this._first = first; | |
| return this; | |
| } | |
| withLast(last: string) { | |
| this._last = last; | |
| return this; | |
| } | |
| toString() { | |
| if (!this._first) { | |
| throw new Error("A first name is required."); | |
| } | |
| if (!this._last) { | |
| throw new Error("A last name is required."); | |
| } | |
| if (this._designation) { | |
| return `${this._designation} ${this._first} ${this._last}`; | |
| } | |
| return `${this._first} ${this._last}`; | |
| } | |
| print() { | |
| console.log(this.toString()); | |
| } | |
| } | |
| // use the simple syntax when all functions are required. | |
| // export type FluentPerson = Fluent<Person>; | |
| // use the verbose syntax when some functions are optional. | |
| export type FluentPerson = Fluent< | |
| Person, | |
| "withFirst" | "withLast", // these keys are required | |
| "withDesignation" // these keys are optional | |
| >; | |
| const person = Person.create() | |
| .withDesignation("Mr.") // this call is optional | |
| .withFirst("John") // this call is required | |
| .withLast("Doe"); // this call is required | |
| // this will be a compile-time error if one of the | |
| // required functions was not called. | |
| person.print(); |
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| export type Fluent< | |
| T, | |
| Required extends keyof T = FluentKeys<T>, | |
| Optional extends keyof T = never, | |
| > = { | |
| [K in Required | Optional]: ChangeReturn< | |
| T[K], | |
| Exclude<Required, K> extends never | |
| ? T | |
| : Fluent<T, Exclude<Required, K>, Exclude<Optional, K>> | |
| >; | |
| }; | |
| export type FluentKeys<T> = { | |
| [K in keyof T]: T[K] extends (...args: any[]) => T ? K : never; | |
| }[keyof T]; | |
| type ChangeReturn<F, Return> = F extends (...args: infer Args) => any | |
| ? (...args: Args) => Return | |
| : never; |
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