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type IsNumber<T> = T extends number ? true : false;

// true
type Example2 = IsNumber<100>
// false
type Example1 = IsNumber<RegExp>

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interface Animal {}
interface Dog extends Animal {}

// boolean
type NestedExample = Dog extends Animal ? (RegExp extends Animal ? number : boolean) : string;

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type ReturnType<T> = T extends (...args: any[]) => infer R ? R : any;


// void
type Example1 = ReturnType<(n: number, s: string) => void>;
// any
type Example2 = ReturnType<number>;

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interface AppConfig {
    username: string;
    layout: string;
};

// layout | username
type AppConfigKeys = keyof AppConfig;

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interface Messenger {
    sendText: () => void;
    sendFile: () => void;
}

type Async<T> = {
    [Property in keyof T]: () => Promise<void>;
};

// type AsyncMessenger = {

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interface Messenger {
    sendText: () => void;
    sendFile: () => void;
}

type Async<T> = {
    [Property in keyof T as Capitalize<Property & string>]: () => Promise<void>;
};

// type AsyncMessenger = {

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type Url = `https://${string}.${string}`;

const url1: Url = 'https://google.com';

// Error: Type 'test' is not assignable to type 'https://${string}.${string}'.
const url2: Url = 'test';

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type Person = {
    name: string;
    [key: `phone${number}`]: string;
};

const userA: Person = {
    name: 'John',
    phone1: '111-111-111',
    phone2: '222-222-222',
};

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interface Messenger {
    sendText: () => void;
    sendFile: () => void;
    checkStatus?: () => void;
}

type RequiredFields<T> = {
    [K in keyof T as T[K] extends Required<T>[K] ? K : never]: T[K];
};