| 1 | <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> |
|---|
| 2 | <html> |
|---|
| 3 | |
|---|
| 4 | <head> |
|---|
| 5 | <meta http-equiv="Content-Language" content="en-us"> |
|---|
| 6 | <meta http-equiv="Content-Type" content="text/html; charset=windows-1252"> |
|---|
| 7 | <meta name="GENERATOR" content="Microsoft FrontPage 5.0"> |
|---|
| 8 | <meta name="ProgId" content="FrontPage.Editor.Document"> |
|---|
| 9 | <title>Boost Library Reuse</title> |
|---|
| 10 | </head> |
|---|
| 11 | |
|---|
| 12 | <body bgcolor="#FFFFFF" text="#000000"> |
|---|
| 13 | |
|---|
| 14 | <table border="1" bgcolor="#007F7F" cellpadding="2"> |
|---|
| 15 | <tr> |
|---|
| 16 | <td bgcolor="#FFFFFF"><img src="../boost.png" alt="boost.png (6897 bytes)" width="277" height="86"></td> |
|---|
| 17 | <td><a href="../index.htm"><font face="Arial" color="#FFFFFF"><big>Home</big></font></a></td> |
|---|
| 18 | <td><a href="../libs/libraries.htm"><font face="Arial" color="#FFFFFF"><big>Libraries</big></font></a></td> |
|---|
| 19 | <td><a href="../people/people.htm"><font face="Arial" color="#FFFFFF"><big>People</big></font></a></td> |
|---|
| 20 | <td><a href="faq.htm"><font face="Arial" color="#FFFFFF"><big>FAQ</big></font></a></td> |
|---|
| 21 | <td><a href="index.htm"><font face="Arial" color="#FFFFFF"><big>More</big></font></a></td> |
|---|
| 22 | </tr> |
|---|
| 23 | </table> |
|---|
| 24 | |
|---|
| 25 | <h1>Boost Library reuse: cost versus benefit trade-offs</h1> |
|---|
| 26 | <p>A Boost library <b>should not</b> use libraries other than Boost or the C++ |
|---|
| 27 | Standard Library.</p> |
|---|
| 28 | <p>A Boost library <b>should</b> use other Boost Libraries or the C++ Standard |
|---|
| 29 | Library, but only when the benefits outweigh the costs. </p> |
|---|
| 30 | <p>The benefits of using components from other libraries may include clearer, |
|---|
| 31 | more understandable code, reduced development and maintenance costs, and the |
|---|
| 32 | assurance which comes from reusing well-known and trusted building blocks.</p> |
|---|
| 33 | <p>The costs may include undesirable coupling between components, and added |
|---|
| 34 | compilation and runtime costs. If the interface to the additional |
|---|
| 35 | component is complex, using it may make code less readable, and thus actually |
|---|
| 36 | increase development and maintenance costs.</p> |
|---|
| 37 | <p>Negative effects of coupling become obvious when one library uses a second |
|---|
| 38 | library which uses a third, and so on. The worst form of coupling requires the |
|---|
| 39 | user understand each of the coupled libraries. Coupling may also reduce the |
|---|
| 40 | portability of a library - even in case when all used libraries are |
|---|
| 41 | self-sufficient (see example of questionable usage of <iostream> library |
|---|
| 42 | below).</p> |
|---|
| 43 | <p><b>Example where another boost component should certainly be used:</b> |
|---|
| 44 | boost::noncopyable (in <a href="../boost/utility.hpp">boost/utility.hpp</a>) has |
|---|
| 45 | considerable benefits; it simplifies code, improves readability, and signals |
|---|
| 46 | intent. Costs are low as coupling is limited; noncopyable itself |
|---|
| 47 | uses no other classes and its header includes only the lightweight headers |
|---|
| 48 | <boost/config.hpp> and <cstddef>. There are no runtime costs |
|---|
| 49 | at all. With costs so low and benefits so high, other boost libraries should use |
|---|
| 50 | boost::noncopyable when the need arises except in exceptional circumstances.</p> |
|---|
| 51 | <p><b>Example where a standard library component might possibly be used:</b> |
|---|
| 52 | Providing diagnostic output as a debugging aid can be a nice feature for a |
|---|
| 53 | library. Yet using Standard Library <iostream> can involves a lot of |
|---|
| 54 | additional cost, particularly if <iostream> is unlikely to be use |
|---|
| 55 | elsewhere in the application. In certain GUI or embedded applications, |
|---|
| 56 | coupling to <iostream> would be a disqualification. |
|---|
| 57 | Consider redesign of the boost library in question so that the user supplies the |
|---|
| 58 | diagnostic output mechanism.</p> |
|---|
| 59 | <p><b>Example where another boost component should not be used:</b> The |
|---|
| 60 | boost dir_it library has considerable coupling and runtime costs, not to mention |
|---|
| 61 | portability issues for unsupported operating systems. While completely |
|---|
| 62 | appropriate when directory iteration is required, it would not be reasonable for |
|---|
| 63 | another boost library to use dir_it just to check that a file is available |
|---|
| 64 | before opening. C++ Standard Library file open functionality does this at |
|---|
| 65 | lower cost. Don't use dir_it just for the sake of using a boost library.</p> |
|---|
| 66 | <hr> |
|---|
| 67 | <p>Revised <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B %Y" startspan -->02 October 2003<!--webbot bot="Timestamp" endspan i-checksum="32277" --></p> |
|---|
| 68 | <p>© Copyright Beman Dawes 2000</p> |
|---|
| 69 | <p>Distributed under the Boost Software License, Version 1.0. (See |
|---|
| 70 | accompanying file <a href="../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or copy |
|---|
| 71 | at <a href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</p> |
|---|
| 72 | |
|---|
| 73 | </body> |
|---|
| 74 | |
|---|
| 75 | </html> |
|---|
