title: are constexpr functions that load files possible in C++?
body: <p>There was a similar question <a href="https://stackoverflow.com/questions/26161422/is-it-possible-to-read-a-file-at-compile-time">here</a> but it had no valuable information so I want to ask this again - is it possible to load contents of an arbitrary file using a <code>constexpr</code> function? I know that this seems impossible since all the possible functions that allow file I/O (<code>fopen</code>, <code>open</code> ...) are not <code>constexpr</code> so cannot be called in this scenario. However - since there are many people here who follow the development of c++17 and on - is there any hope that further standards will include some file I/O API that will be <code>constexpr</code> and could be used to load a file at compile time?</p>
  
  <p>Just for a comparison - Haxe allows to do almost anything via the compile time macros, so it would be very cool to have something similar in C++. For example, generating class instances by deserializing files.</p>