title: What compile speed improvement can I expect with modules in Visual Studio 2015
body: <p>Visual Studio 2015 <a href="https://blogs.msdn.microsoft.com/vcblog/2015/12/03/c-modules-in-vs-2015-update-1/" rel="nofollow">supports modules</a>. I'm excited about this feature, and although I know it has important implications over and above build time, that's my interest right now. I'm thinking of larger code bases of the order of half a million lines of code or more, which have a lot of <code>#include</code>s in header files.</p>
  
  <p>My previous approach to this would have been to manually or automatically remove the unnecessary includes in favor of forward declarations, etc, and then use precompiled headers. The result would typically be a significant improvement in build times, from memory of the order of 2-3 times. Now it seems like I should consider using modules, which might be a lot less effort and deliver arguably a better engineered and more future-proof solution.</p>
  
  <p>Can anyone comment as to the potential effect on compile speed of going down the module route instead, for larger code bases measured in 100s of thousands or millions of lines of code?</p>