angular-docs-cn/public/docs/js/latest/api/di/OptionalMetadata-class.jade

p.location-badge.
  exported from <a href='../di'>angular2/di</a>
  defined in <a href="https://github.com/angular/angular/tree/2.0.0-alpha.34/modules/angular2/src/di/metadata.ts#L17-L34">angular2/src/di/metadata.ts (line 17)</a>

:markdown
  A parameter metadata that marks a dependency as optional. <a href='Injector-class.html'><code>Injector</code></a> provides `null` if
  the dependency is not found.
  
  ```
  class AComponent {
    constructor(@Optional() aService:MyService) {
      this.aService = aService;
    }
  }
  ```
  
  

.l-main-section
  h2 Annotations
  .l-sub-section
    h3.annotation CONST
    pre.prettyprint
      code.
        @CONST()


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  h2 Members
  .l-sub-section
    h3 toString

    
    pre.prettyprint
      code.
        toString()
    
    :markdown