wed/standalone/lib/external/rxjs/internal/observable/iif.js

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define(function(require,exports,module){

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
var defer_1 = require("./defer");
var empty_1 = require("./empty");
/**
 * Decides at subscription time which Observable will actually be subscribed.
 *
 * <span class="informal">`If` statement for Observables.</span>
 *
 * `if` accepts a condition function and two Observables. When
 * an Observable returned by the operator is subscribed, condition function will be called.
 * Based on what boolean it returns at that moment, consumer will subscribe either to
 * the first Observable (if condition was true) or to the second (if condition was false). Condition
 * function may also not return anything - in that case condition will be evaluated as false and
 * second Observable will be subscribed.
 *
 * Note that Observables for both cases (true and false) are optional. If condition points to an Observable that
 * was left undefined, resulting stream will simply complete immediately. That allows you to, rather
 * then controlling which Observable will be subscribed, decide at runtime if consumer should have access
 * to given Observable or not.
 *
 * If you have more complex logic that requires decision between more than two Observables, {@link defer}
 * will probably be a better choice. Actually `if` can be easily implemented with {@link defer}
 * and exists only for convenience and readability reasons.
 *
 *
 * @example <caption>Change at runtime which Observable will be subscribed</caption>
 * let subscribeToFirst;
 * const firstOrSecond = Rx.Observable.if(
 *   () => subscribeToFirst,
 *   Rx.Observable.of('first'),
 *   Rx.Observable.of('second')
 * );
 *
 * subscribeToFirst = true;
 * firstOrSecond.subscribe(value => console.log(value));
 *
 * // Logs:
 * // "first"
 *
 * subscribeToFirst = false;
 * firstOrSecond.subscribe(value => console.log(value));
 *
 * // Logs:
 * // "second"
 *
 *
 * @example <caption>Control an access to an Observable</caption>
 * let accessGranted;
 * const observableIfYouHaveAccess = Rx.Observable.if(
 *   () => accessGranted,
 *   Rx.Observable.of('It seems you have an access...') // Note that only one Observable is passed to the operator.
 * );
 *
 * accessGranted = true;
 * observableIfYouHaveAccess.subscribe(
 *   value => console.log(value),
 *   err => {},
 *   () => console.log('The end')
 * );
 *
 * // Logs:
 * // "It seems you have an access..."
 * // "The end"
 *
 * accessGranted = false;
 * observableIfYouHaveAccess.subscribe(
 *   value => console.log(value),
 *   err => {},
 *   () => console.log('The end')
 * );
 *
 * // Logs:
 * // "The end"
 *
 * @see {@link defer}
 *
 * @param {function(): boolean} condition Condition which Observable should be chosen.
 * @param {Observable} [trueObservable] An Observable that will be subscribed if condition is true.
 * @param {Observable} [falseObservable] An Observable that will be subscribed if condition is false.
 * @return {Observable} Either first or second Observable, depending on condition.
 * @static true
 * @name iif
 * @owner Observable
 */
function iif(condition, trueResult, falseResult) {
    if (trueResult === void 0) { trueResult = empty_1.EMPTY; }
    if (falseResult === void 0) { falseResult = empty_1.EMPTY; }
    return defer_1.defer(function () { return condition() ? trueResult : falseResult; });
}
exports.iif = iif;
//# sourceMappingURL=iif.js.map
return module.exports;

});