TypeScript/src/compiler/corePublic.ts

namespace ts {
    // WARNING: The script `configurePrerelease.ts` uses a regexp to parse out these values.
    // If changing the text in this section, be sure to test `configurePrerelease` too.
    export const versionMajorMinor = "4.6";
    // The following is baselined as a literal template type without intervention
    /** The version of the TypeScript compiler release */
    // eslint-disable-next-line @typescript-eslint/no-inferrable-types
    export const version: string = `${versionMajorMinor}.0-dev`;

    /**
     * Type of objects whose values are all of the same type.
     * The `in` and `for-in` operators can *not* be safely used,
     * since `Object.prototype` may be modified by outside code.
     */
    export interface MapLike<T> {
        [index: string]: T;
    }

    export interface SortedReadonlyArray<T> extends ReadonlyArray<T> {
        " __sortedArrayBrand": any;
    }

    export interface SortedArray<T> extends Array<T> {
        " __sortedArrayBrand": any;
    }

    /** Common read methods for ES6 Map/Set. */
    export interface ReadonlyCollection<K> {
        readonly size: number;
        has(key: K): boolean;
        keys(): Iterator<K>;
    }

    /** Common write methods for ES6 Map/Set. */
    export interface Collection<K> extends ReadonlyCollection<K> {
        delete(key: K): boolean;
        clear(): void;
    }

    /** ES6 Map interface, only read methods included. */
    export interface ReadonlyESMap<K, V> extends ReadonlyCollection<K> {
        get(key: K): V | undefined;
        values(): Iterator<V>;
        entries(): Iterator<[K, V]>;
        forEach(action: (value: V, key: K) => void): void;
    }

    /**
     * ES6 Map interface, only read methods included.
     */
    export interface ReadonlyMap<T> extends ReadonlyESMap<string, T> {
    }

    /** ES6 Map interface. */
    export interface ESMap<K, V> extends ReadonlyESMap<K, V>, Collection<K> {
        set(key: K, value: V): this;
    }

    /**
     * ES6 Map interface.
     */
    export interface Map<T> extends ESMap<string, T> {
    }

    /* @internal */
    export interface MapConstructor {
        // eslint-disable-next-line @typescript-eslint/prefer-function-type
        new <K, V>(iterable?: readonly (readonly [K, V])[] | ReadonlyESMap<K, V>): ESMap<K, V>;
    }

    /** ES6 Set interface, only read methods included. */
    export interface ReadonlySet<T> extends ReadonlyCollection<T> {
        has(value: T): boolean;
        values(): Iterator<T>;
        entries(): Iterator<[T, T]>;
        forEach(action: (value: T, key: T) => void): void;
    }

    /** ES6 Set interface. */
    export interface Set<T> extends ReadonlySet<T>, Collection<T> {
        add(value: T): this;
        delete(value: T): boolean;
    }

    /* @internal */
    export interface SetConstructor {
        // eslint-disable-next-line @typescript-eslint/prefer-function-type
        new <T>(iterable?: readonly T[] | ReadonlySet<T>): Set<T>;
    }

    /** ES6 Iterator type. */
    export interface Iterator<T> {
        next(): { value: T, done?: false } | { value: void, done: true };
    }

    /** Array that is only intended to be pushed to, never read. */
    export interface Push<T> {
        push(...values: T[]): void;
        /* @internal*/ readonly length: number;
    }

    /* @internal */
    export type EqualityComparer<T> = (a: T, b: T) => boolean;

    /* @internal */
    export type Comparer<T> = (a: T, b: T) => Comparison;

    /* @internal */
    export const enum Comparison {
        LessThan    = -1,
        EqualTo     = 0,
        GreaterThan = 1
    }

    /* @internal */
    namespace NativeCollections {
        declare const Map: MapConstructor | undefined;
        declare const Set: SetConstructor | undefined;

        /**
         * Returns the native Map implementation if it is available and compatible (i.e. supports iteration).
         */
        export function tryGetNativeMap(): MapConstructor | undefined {
            // Internet Explorer's Map doesn't support iteration, so don't use it.
            // eslint-disable-next-line no-in-operator
            return typeof Map !== "undefined" && "entries" in Map.prototype && new Map([[0, 0]]).size === 1 ? Map : undefined;
        }

        /**
         * Returns the native Set implementation if it is available and compatible (i.e. supports iteration).
         */
        export function tryGetNativeSet(): SetConstructor | undefined {
            // Internet Explorer's Set doesn't support iteration, so don't use it.
            // eslint-disable-next-line no-in-operator
            return typeof Set !== "undefined" && "entries" in Set.prototype && new Set([0]).size === 1 ? Set : undefined;
        }
    }

    /* @internal */
    export const Map = getCollectionImplementation("Map", "tryGetNativeMap", "createMapShim");
    /* @internal */
    export const Set = getCollectionImplementation("Set", "tryGetNativeSet", "createSetShim");

    /* @internal */
    type GetIteratorCallback = <I extends readonly any[] | ReadonlySet<any> | ReadonlyESMap<any, any> | undefined>(iterable: I) => Iterator<
        I extends ReadonlyESMap<infer K, infer V> ? [K, V] :
        I extends ReadonlySet<infer T> ? T :
        I extends readonly (infer T)[] ? T :
        I extends undefined ? undefined :
        never>;

    /* @internal */
    function getCollectionImplementation<
        K1 extends MatchingKeys<typeof NativeCollections, () => any>,
        K2 extends MatchingKeys<typeof ShimCollections, (getIterator?: GetIteratorCallback) => ReturnType<(typeof NativeCollections)[K1]>>
    >(name: string, nativeFactory: K1, shimFactory: K2): NonNullable<ReturnType<(typeof NativeCollections)[K1]>> {
        // NOTE: ts.ShimCollections will be defined for typescriptServices.js but not for tsc.js, so we must test for it.
        const constructor = NativeCollections[nativeFactory]() ?? ShimCollections?.[shimFactory](getIterator);
        if (constructor) return constructor as NonNullable<ReturnType<(typeof NativeCollections)[K1]>>;
        throw new Error(`TypeScript requires an environment that provides a compatible native ${name} implementation.`);
    }
}