p.
  <span class="location-badge">exported from <a href="/angular2/di">angular2/di</a></span>
  defined in <a href="https://github.com/angular/angular/tree/master/modules/angular2/src/di/key.js#L17">angular2/src/di/key.js (line 17)</a>

:markdown
  A unique object used for retrieving items from the <a href="angular2/di/Injector-class"><code>Injector</code></a>.
  
  Keys have:
  - a system-wide unique `id`.
  - a `token`, usually the `Type` of the instance.
  
  Keys are used internally by the <a href="angular2/di/Injector-class"><code>Injector</code></a> because their system-wide unique `id`s allow the
  injector to index in arrays rather than looking up items in maps.
  
.l-main-section
  h2 Members
  .l-sub-section
    h3 constructor

    
    pre.prettyprint
      code.
        constructor(token, id)
    
    :markdown
      




  .l-sub-section
    h3 get

    
    pre.prettyprint
      code.
        get(token)
    
    :markdown
      Retrieves a `Key` for a token.





  .l-sub-section
    h3 id

    
    :markdown
      





  .l-sub-section
    h3 metadata

    
    :markdown
      





  .l-sub-section
    h3 numberOfKeys

    
    :markdown
      





  .l-sub-section
    h3 token

    
    :markdown