[boost] mistaken uses of <iostream>

From: Howard Hinnant (hinnant_at_[hidden])
Date: 2006-11-18 10:20:22

<iostream> is the only C++ header that extracts a cost simply by  
including it (in typical implementations).  The usual implementation  
is for it to include a static object of type std::ios_base::Init  
which is responsible for initializing the 8 terminal streams (cin,  
cout, cerr, clog, wcin, wcout, wcerr, wclog).

I've always thought it good programming practice to avoid including  
<iostream> if the translation unit didn't actually need one of these  
8 terminal streams.  For example if I needed to just get to istream  
and ostream to write my own I/O I would include <istream> and  
<ostream> but not <iostream> (the naming is very unfortunate).

It has recently come to my attention that I could be overly sensitive  
to this issue and making a fuss about nothing.  So I'm writing here  
for a reality check.  Do boost programmers consider the use of  
<iostream> as a short cut to get to non-terminal-streams I/O a  
reasonable technique?  Or do boost programmers feel that use of  
<iostream> should be reserved only when using one or more of cin,  
cout, cerr, clog, wcin, wcout, wcerr, wclog?

I did a brief survey of boost 1.33.1 and found many "relaxed" uses of  
<iostream> under the boost/ directory (i.e. non test-case code).  So  
in practice it does appear that using <iostream> as a shortcut is  
considered acceptable practice.  However I wanted to highlight the  
point just in case people do view this as a bug that has simply snuck  
in under the radar to date.

-Howard