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https://github.com/angular/angular
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1eea2b254e
It is possible for a class defined first to be referencing a class defined later, and as a result at the time of the definition it is not possible to access the later's class reference. This allows to refer to the later defined class through a closure.Closes #1891
50 lines
1.3 KiB
TypeScript
50 lines
1.3 KiB
TypeScript
import {Type} from 'angular2/src/facade/lang';
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export interface ForwardRefFn { (): Type; }
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/**
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* Allows to refer to references which are not yet defined.
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*
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* This situation arises when the key which we need te refer to for the purposes of DI is declared,
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* but not yet defined.
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*
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* ## Example:
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*
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* ```
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* class Door {
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* // Incorrect way to refer to a reference which is defined later.
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* // This fails because `Lock` is undefined at this point.
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* constructor(lock:Lock) { }
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*
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* // Correct way to refer to a reference which is defined later.
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* // The reference needs to be captured in a closure.
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* constructor(@Inject(forwardRef(() => Lock)) lock:Lock) { }
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* }
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*
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* // Only at this point the lock is defined.
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* class Lock {
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* }
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* ```
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*
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* @exportedAs angular2/di
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*/
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export function forwardRef(forwardRefFn: ForwardRefFn): Type {
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(<any>forwardRefFn).__forward_ref__ = forwardRef;
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return (<Type><any>forwardRefFn);
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}
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/**
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* Lazily retrieve the reference value.
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*
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* See: {@link forwardRef}
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*
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* @exportedAs angular2/di
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*/
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export function resolveForwardRef(type: any): any {
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if (typeof type == 'function' && type.hasOwnProperty('__forward_ref__') &&
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type.__forward_ref__ === forwardRef) {
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return (<ForwardRefFn>type)();
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} else {
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return type;
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}
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}
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