types-belt/dist/types/function.d.ts

A comprehensive collection of TypeScript utility types for building robust and maintainable applications

/**
 * Function utility types for TypeScript
 * @module FunctionTypes
 */
/**
 * Extracts the return type of a function type
 * @template T - The function type
 * @example
 * ```typescript
 * type MyFunction = () => string;
 * type ReturnType = ReturnType<MyFunction>; // string
 *
 * type AsyncFunction = () => Promise<number>;
 * type AsyncReturnType = ReturnType<AsyncFunction>; // Promise<number>
 * ```
 */
export type ReturnType<T extends (...args: any) => any> = T extends (...args: any) => infer R ? R : any;
/**
 * Extracts the parameter types of a function type
 * @template T - The function type
 * @example
 * ```typescript
 * type MyFunction = (name: string, age: number) => void;
 * type Params = Parameters<MyFunction>; // [string, number]
 *
 * type NoParams = () => void;
 * type NoParamsType = Parameters<NoParams>; // []
 * ```
 */
export type Parameters<T extends (...args: any) => any> = T extends (...args: infer P) => any ? P : never;
/**
 * Extracts the first parameter type of a function
 * @template T - The function type
 * @example
 * ```typescript
 * type MyFunction = (name: string, age: number) => void;
 * type FirstParam = FirstParameter<MyFunction>; // string
 *
 * type NoParams = () => void;
 * type NoFirstParam = FirstParameter<NoParams>; // never
 * ```
 */
export type FirstParameter<T extends (...args: any) => any> = Parameters<T>[0];
/**
 * Extracts the last parameter type of a function
 * @template T - The function type
 * @example
 * ```typescript
 * type MyFunction = (name: string, age: number) => void;
 * type LastParam = LastParameter<MyFunction>; // number
 *
 * type NoParams = () => void;
 * type NoLastParam = LastParameter<NoParams>; // never
 * ```
 */
export type LastParameter<T extends (...args: any) => any> = Parameters<T> extends [...any[], infer L] ? L : never;
/**
 * Creates a function type that takes no parameters
 * @template R - The return type
 * @example
 * ```typescript
 * type NoParamsFunction = NoParamsFunction<string>; // () => string
 * ```
 */
export type NoParamsFunction<R = any> = () => R;
/**
 * Creates a function type that takes a single parameter
 * @template T - The parameter type
 * @template R - The return type
 * @example
 * ```typescript
 * type StringFunction = SingleParamFunction<string, number>; // (param: string) => number
 * ```
 */
export type SingleParamFunction<T = any, R = any> = (param: T) => R;
/**
 * Creates a function type that takes two parameters
 * @template T1 - The first parameter type
 * @template T2 - The second parameter type
 * @template R - The return type
 * @example
 * ```typescript
 * type MathFunction = TwoParamFunction<number, number, number>; // (a: number, b: number) => number
 * ```
 */
export type TwoParamFunction<T1 = any, T2 = any, R = any> = (param1: T1, param2: T2) => R;
/**
 * Creates a function type that takes any number of parameters
 * @template T - The parameter types
 * @template R - The return type
 * @example
 * ```typescript
 * type VariadicFunction = VariadicFunction<string | number, boolean>; // (...args: (string | number)[]) => boolean
 * ```
 */
export type VariadicFunction<T = any, R = any> = (...args: T[]) => R;
/**
 * Makes a function type's parameters optional
 * @template T - The function type
 * @example
 * ```typescript
 * type RequiredFunction = (name: string, age: number) => void;
 * type OptionalFunction = OptionalParameters<RequiredFunction>; // (name?: string, age?: number) => void
 * ```
 */
export type OptionalParameters<T extends (...args: any) => any> = T extends (...args: infer P) => infer R ? (...args: {
    [K in keyof P]?: P[K];
}) => R : never;
/**
 * Creates a function type that returns void
 * @template T - The parameter types
 * @example
 * ```typescript
 * type VoidFunction = VoidFunction<string, number>; // (a: string, b: number) => void
 * ```
 */
export type VoidFunction<T extends any[] = any[]> = (...args: T) => void;
/**
 * Creates a function type that returns a Promise
 * @template T - The parameter types
 * @template R - The resolved type
 * @example
 * ```typescript
 * type AsyncFunction = AsyncFunction<string, number>; // (param: string) => Promise<number>
 * ```
 */
export type AsyncFunction<T extends any[] = any[], R = any> = (...args: T) => Promise<R>;
/**
 * Extracts the type of a method from an object type
 * @template T - The object type
 * @template K - The method key
 * @example
 * ```typescript
 * interface User {
 *   getName(): string;
 *   getAge(): number;
 * }
 *
 * type GetNameMethod = MethodType<User, 'getName'>; // () => string
 * ```
 */
export type MethodType<T, K extends keyof T> = T[K] extends (...args: any[]) => any ? T[K] : never;
/**
 * Creates a function type that can be called with or without parameters
 * @template T - The parameter types
 * @template R - The return type
 * @example
 * ```typescript
 * type FlexibleFunction = FlexibleFunction<string, number>; // (param?: string) => number
 * ```
 */
export type FlexibleFunction<T = any, R = any> = (param?: T) => R;
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