Should I use interfaces here?

<p>I&#39;m writing a small terminal utility that provides definition, translation and other actions and I have to use many api, also I need a way to replace the apis if needed, and while trying to write tests for this I feel I got it all wrong.</p> <p>Gist: <a href="https://gist.github.com/taosx/4b615381456561da797ac55fd17e981b" rel="nofollow">https://gist.github.com/taosx/4b615381456561da797ac55fd17e981b</a></p> <pre><code>package main import ( &#34;fmt&#34; &#34;log&#34; &#34;net/url&#34; &#34;strings&#34; &#34;github.com/valyala/fasthttp&#34; ) // API is our main struct, it helps create our url in any way we like and returns a string // It is a must to provide the url string like this: api := API{url: &#34;http://api.baseurl.com&#34;} type API struct { api *url.URL url string } func (a *API) String() interface{} { return a.api } // Create function fills our url.URL type by using the url in struct API func (a *API) Create() *API { api, err := url.Parse(a.url) if err != nil { log.Fatal(&#34;[ERR] &#34;, err) } a.api = api return a } // Suffix function adds our path to our api func (a *API) Suffix(suffixes ...string) *API { if len(suffixes) &lt; 1 { fmt.Println(&#34;Can&#39;t leave suffix empty&#34;) return a } a.api.Path += strings.Join(suffixes, &#34;/&#34;) return a } // Query function adds our queries to our api func (a *API) Query(query url.Values) *API { if len(query) &lt; 1 { fmt.Println(&#34;Can&#39;t leave query empty&#34;) return a } q := a.api.Query() for k, v := range query { if len(v) &gt; 1 { v := strings.Join(v, &#34;,&#34;) q.Add(k, v) } else { q.Add(k, v[0]) } } encQuery := q.Encode() escQuery, _ := url.QueryUnescape(encQuery) a.api.RawQuery += escQuery return a } // Get makes a request to the url crafted and returns: &lt;status code&gt;, &lt;response/body&gt;, &lt;error(if any or nil otherwise)&gt; func (a *API) Get() (int, []byte, error) { urlstr := a.api.String() saved := []byte{} status, body, err := fasthttp.Get(saved, urlstr) if err != nil { fmt.Println(&#34;Error:&#34;, err) return status, nil, err } return status, body, err } </code></pre> <hr/>**评论：**<br/><br/>sethammons: <pre><p>do you mean here?</p> <pre><code>func (a *API) String() interface{} { return a.api } </code></pre> <p>I wouldn&#39;t. I would <code>func (a *API) String() string</code> because that is typically what a <code>String()</code> method does. If you want to have an accessor for getting at <code>a.api</code>, you could have <code>func (a *API) URL() *url.URL</code>. If you find that you need something that is not specific (ie, you wont always return <code>*url.URL</code>, then use an interface. See <a href="http://go-book.appspot.com/interfaces.html" rel="nofollow">http://go-book.appspot.com/interfaces.html</a> for an example of that. Cheers!</p></pre>