title: Error "can't load package: package my_prog: found packages my_prog and main"
body: <p>In my GOPATH I have something like this:</p>
  
  <pre><code>/bin/
  /pkg/
  /src/
  /src/my_prog/
  /src/my_prog/main.go
  /src/my_prog/d_interface.go
  /src/my_prog/d_struct_that_implements_the_interface.go
  </code></pre>
  
  <p>In <code>main.go</code> I have <code>package main</code>, in <code>d_interface.go</code> and <code>d_struct_that_implements_the_interface.go</code> I have <code>package my_prog</code>.</p>
  
  <p>When I try to <code>go build my_prog</code> I get the following error:</p>
  
  <pre><code>can't load package: package my_prog: found packages my_prog (d_interface.go) and main (main.go) in C:\dev\Code\Go\src\my_prog
  </code></pre>
  
  <p>Does this mean that any file that belongs to <code>package main</code> should go in its own folder? If so, what is the reason for this?</p>