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Subject: [boost] Header Inclusion practices
From: Robert Ramey (ramey_at_[hidden])
Date: 2017-04-11 17:55:58

As long as I can remember, it's been my practice to write program code
to minimize dependencies on the environment in which it is built. By
environment I mean things external to the code itself like environmental
and command line variables, directory context etc. As part of this I
use rules for header file inclusion:

a) use #include "header.hpp" for files in the same directory as the
current source file.

b) use #include "other directory/header.hpp" for files which are known
to be in a specific place relative to the current file. This shows up
in things like: #include "../include/header.hpp" for tests and examples.

c) use #include <boost/serialization/xml_archive.hpp> for files which
are found by looking in directories listed in "-I" switches and
environmental variables (INCLUDE). I generally try not to depend upon
any environmental variables as I always forget to set them or even how
to set them. Come to think about it. I don't know how my build system
finds the boost libraries. I presume it's through some IDE/Bjam/CMake
setting which I can never remember.

d) use #include <iostream> for standard library components. Presumably
these are routed to some directory relative to the compiler.

So some of my source files look like:

// interval.hpp header for safe numerics library

#include <limits>
#include <cassert>
#include <type_traits>
#include <array>
#include <initializer_list>

#include <boost/logic/tribool.hpp>
#include <boost/core/demangle.hpp>

#include "utility.hpp" // log
#include "checked_result.hpp"
#include "checked.hpp"


// example using he safe numerics library

#include <iostream>
#include <limits>
#include <boost/integer.hpp>

#include "../include/cpp.hpp"
#include "../include/exception.hpp"
#include "../include/safe_integer.hpp"
#include "../include/safe_range.hpp"

This has raised consternation in some quarters - but I don't see
anything wrong with it. It basically means that only the <boost
libraries are depended on the whole b2 business. I didn't want the
incubator version of the the safe numeric library to depend on the
library having been accepted into boost have have b2 run. Also I don't
like adding the library to boost - and having to change all the headers.
  What if someone want's to run the tests/examples outside of the boost

As far as I know this question has never been asked before and I'm
curious to know what others might have to say about this.

Robert Ramey

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