39 lines
1000 B
TypeScript
39 lines
1000 B
TypeScript
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/*---------------------------------------------------------------------------------------------
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* Copyright (c) Microsoft Corporation. All rights reserved.
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* Licensed under the MIT License. See License.txt in the project root for license information.
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*--------------------------------------------------------------------------------------------*/
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export interface Lazy<T> {
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readonly value: T;
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readonly hasValue: boolean;
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map<R>(f: (x: T) => R): Lazy<R>;
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}
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class LazyValue<T> implements Lazy<T> {
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private _hasValue: boolean = false;
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private _value?: T;
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constructor(
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private readonly _getValue: () => T
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) { }
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get value(): T {
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if (!this._hasValue) {
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this._hasValue = true;
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this._value = this._getValue();
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}
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return this._value!;
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}
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get hasValue(): boolean {
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return this._hasValue;
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}
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public map<R>(f: (x: T) => R): Lazy<R> {
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return new LazyValue(() => f(this.value));
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}
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}
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export function lazy<T>(getValue: () => T): Lazy<T> {
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return new LazyValue<T>(getValue);
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}
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