title: Vuex reactive mapGetters with arguments passed through
body: <p>I have lots of getters that pass arguments to the store such as:</p>
  
  <pre><code>this.$store.getters['getSomeThing'](this.id)
  </code></pre>
  
  <p>And I'm not finding recommendations for how to optimally use <code>mapGetters</code> to maintain reactivity, while passing the arguments through. One suggestion I found was to map the getter and then pass the argument in mounted:</p>
  
  <pre><code>computed: {  
    ...mapGetters([
      'getSomeThing'
    ])
  },
  mounted () {
    this.getSomeThing(this.id)
  }
  </code></pre>
  
  <p>This really seems to be sub-optimal, as it would only check for a change to state on mounted. Any suggestions for how to best maintain reactivity while passing an argument to a getter? Here's an example of a getter that would match the above code:</p>
  
  <pre><code>getSomeThing: (state) =&gt; (id) =&gt; {
    return state.things.find(t =&gt; { return t.id === id })
  }
  </code></pre>