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<title>Design Notes</title>
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<link rel="home" href="../index.html" title="Chapter 1. The Boost Convert Library 2.0">
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<link rel="up" href="../index.html" title="Chapter 1. The Boost Convert Library 2.0">
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<link rel="prev" href="convert_motivation.html" title="Motivation">
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<div class="section">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="the_boost_convert_library.convert_design"></a><a class="link" href="convert_design.html" title="Design Notes">Design Notes</a>
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</h2></div></div></div>
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<p>
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Unlike monolithic Convert.V1 (submitted for a review and ultimately withdrawn
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about three years ago) this V2 version takes a different route. Design-wise,
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it follows the successful design of <span class="emphasis"><em>boost::lexical_cast</em></span>
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which provides
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="disc">
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<li class="listitem">
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a uniform API facade to deploy the relevant functionalty and
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</li>
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<li class="listitem">
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the means to plug a particular type in to the <span class="emphasis"><em>boost::lexical_cast</em></span>
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framework; namely, <span class="emphasis"><em>operator>>(std::istream&)</em></span>
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and <span class="emphasis"><em>operator<<(std::ostream&)</em></span>).
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</li>
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</ul></div>
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<p>
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The <span class="emphasis"><em>Boost.Convert</em></span> follows that design and consists of
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two components
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="disc">
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<li class="listitem">
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the <span class="emphasis"><em>Boost.Convert</em></span> API facade to provide simple, minimal
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and uniform deployment interface;
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</li>
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<li class="listitem">
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the extendible library of pluggable converters to provide various type
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conversions and transformations with varying configurability and performance.
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</li>
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</ul></div>
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<p>
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The API facade implements familiar and new conversion/transformation-related
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behavior such as:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="disc">
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<li class="listitem">
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configurable throwing and non-throwing failed-conversion behavior;
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</li>
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<li class="listitem">
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support for the default/fallback value to be returned when conversion/transformation
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fails;
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</li>
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<li class="listitem">
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two types of the conversion-failure check - basic/simple and better/safe;
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</li>
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<li class="listitem">
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no <span class="emphasis"><em>Default Constructibility</em></span> requirement for the Target/Destination
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type;
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</li>
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<li class="listitem">
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support for standard algorithms.
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</li>
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</ul></div>
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<p>
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The library of pluggable converters does not depend on the <span class="emphasis"><em>Boost.Convert</em></span>
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API facade and is expected to be extended over time. At the moment with the
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current proposal only two proof-of-the-concept converters are supplied -- string-to-type
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(and type-to-string) <span class="emphasis"><em>boost::lexical_cast</em></span>-based and <span class="emphasis"><em>std::stringstream</em></span>-based
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converters.
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</p>
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<p>
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The <span class="emphasis"><em>boost::lexical_cast</em></span>-based converter demonstrates how
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independent conversion libraries might be incorporated in to the <span class="emphasis"><em>Boost.Convert</em></span>
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framework.
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</p>
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<p>
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The <span class="emphasis"><em>std::stringstream</em></span>-based converter draws on the standard
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<span class="emphasis"><em>std::streams</em></span>-provided functionality it offers:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="disc">
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<li class="listitem">
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formatting support (like <span class="emphasis"><em>std::hex</em></span>, <span class="emphasis"><em>std::scientific</em></span>,
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etc.);
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</li>
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<li class="listitem">
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support for different locales;
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</li>
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<li class="listitem">
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<span class="emphasis"><em>char</em></span> and <span class="emphasis"><em>wchar_t</em></span> support.
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</li>
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</ul></div>
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<p>
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The latter converter is based on std::stringstream and is far from being a
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speed devil. However, it might be quite useful and sufficient for applications
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with moderate performance-related but extensive formatting, locale, processing
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flow, etc. requirements. Otherwise, a different converter (say, built on <span class="emphasis"><em>Boost.Spirit</em></span>)
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might be plugged in and deployed instead as demonstrated by the <span class="emphasis"><em>boost::lexical_cast</em></span>-based
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converter.
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</p>
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<p>
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An interesting side-effect of the described design is that <span class="emphasis"><em>Boost.Convert</em></span>
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is not limited to string-to-type and type-to-string conversions. In fact, the
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<span class="emphasis"><em>Boost.Convert</em></span> API facade is type-agnostic. Actually supported
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types are defined by the respective plugged converter. Consequently, a wide
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range of conversion/transformation-related tasks can be addressed and deployed
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uniformly. For example, encryption by a string-to-string encrypting converter,
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etc.
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</p>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<td align="right"><div class="copyright-footer">Copyright © 2009-2014 Vladimir Batov<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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</p>
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</div></td>
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</tr></table>
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<hr>
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<div class="spirit-nav">
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<a accesskey="p" href="convert_motivation.html"><img src="../images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../images/home.png" alt="Home"></a><a accesskey="n" href="convert_started.html"><img src="../images/next.png" alt="Next"></a>
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