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diff --git a/src/third_party/boost/libs/filesystem/v3/doc/v3_design.html b/src/third_party/boost/libs/filesystem/v3/doc/v3_design.html new file mode 100644 index 00000000000..c5204fff854 --- /dev/null +++ b/src/third_party/boost/libs/filesystem/v3/doc/v3_design.html @@ -0,0 +1,192 @@ +<html> + +<head> +<meta http-equiv="Content-Language" content="en-us"> +<meta name="GENERATOR" content="Microsoft FrontPage 5.0"> +<meta name="ProgId" content="FrontPage.Editor.Document"> +<meta http-equiv="Content-Type" content="text/html; charset=windows-1252"> +<title>Filesystem V3 Design</title> +<link rel="stylesheet" type="text/css" href="../../../../doc/src/minimal.css"> +</head> + +<body> + +<table border="0" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111"> + <tr> + <td> +<a href="../../../../index.htm"> +<img src="../../../../boost.png" alt="boost.png (6897 bytes)" align="middle" border="0" width="300" height="86"></a></td> + <td align="middle"> + <font size="7">Filesystem Version 3<br> + Design</font></td> + </tr> +</table> + +<table border="0" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF" width="100%"> + <tr> + <td><a href="index.htm">Filesystem Home</a> + <a href="release_history.html">Releases</a> + <a href="reference.html">Reference</a> + <a href="tutorial.html">Tutorial</a> + <a href="faq.htm">FAQ</a> + <a href="portability_guide.htm">Portability</a> + <a href="v3.html">V3 Intro</a> + <a href="v3_design.html">V3 Design</a> + <a href="deprecated.html">Deprecated</a> + </td> + </tr> +</table> + +<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" align="right"> + <tr> + <td width="100%" bgcolor="#D7EEFF" align="center"> + <i><b>Contents</b></i></td> + </tr> + <tr> + <td width="100%" bgcolor="#E8F5FF"> + <a href="#Introduction">Introduction</a><br> + <a href="#Problem">Problem</a><br> + <a href="#Solution">Solution</a><br> + <a href="#Details">Details</a><br> + <a href="#Other-changes">Other changes</a><br> + <a href="#Acknowledgements">Acknowledgements</a></td> + </tr> + </table> + +<p><b>Caution:</b> This page documents thinking early in the V3 development +process, and is intended to serve historical purposes. It is not updated to +reflect the current state of the library.</p> + +<h2><a name="Introduction">Introduction</a></h2> + +<p>During the review of Boost.Filesystem.V2 (Internationalization), Peter Dimov +suggested that the<code> basic_path</code> class template was unwieldy, and that a single +path type that accommodated multiple character types and encodings would be more +flexible. Although I wasn't willing to stop development at that time to +explore how this idea might be implemented, or to break from the pattern for +Internationalization used the C++ standard library, I've often thought about +Peter's suggestion. With the advent of C++0x <code>char16_t</code> and <code>char32_t</code> character +types, the <code>basic_path</code> class template approach becomes even more unwieldy, so it +is time to revisit the problem in light of Peter's suggestion.</p> + +<h2><b><a name="Problem">Problem</a></b></h2> + +<p>With Filesystem.V2, a path argument to a user defined function that is to +accommodate multiple character types and encodings must be written as a +template. Do-the-right-thing overloads or template metaprogramming must be +employed to allow arguments to be written as string literals. Here's what it +looks like:</p> + +<blockquote> + <pre>template<class Path> +void foo( const Path & p );</pre> + <pre>inline void foo( const path & p ) +{ + return foo<path>( p ); +} +inline void foo( const wpath & p ) +{ + return foo<wpath>( p ); +}</pre> +</blockquote> +<p>That's really ugly for such a simple need, and there would be a combinatorial +explosion if the function took multiple Path arguments and each could be either +narrow or wide. It gets even worse if the C++0x <code>char16_t</code> and <code> +char32_t</code> types are to be supported.</p> + +<h2><a name="Solution">Solution</a></h2> + +<p>Overview:</p> + +<ul> + <li>A single, non-template, <code>class path</code>.</li> + <li>Each member function is a template accommodating the various + applicable character types, including user-defined character types.</li> + <li>Hold the path internally in a string of the type used by the operating + system API; <code>std::string</code> for POSIX, <code>std::wstring</code> for Windows.</li> +</ul> + +<p>The signatures presented in <a href="#Problem">Problem</a> collapse to +simply:</p> +<blockquote> + <pre>void foo( const path & p );</pre> +</blockquote> + +<p>That's a signification reduction in code complexity. Specification becomes +simpler, too. I believe it will be far easier to teach, and result in much more +flexible user code.</p> + +<p>Other benefits:</p> +<ul> + <li>All the polymorphism still occurs at compile time.</li> + <li>Efficiency is increased, in that conversions of the encoding, if required, + only occur once at the time of creation, not each time the path is used.</li> + <li>The size of the implementation code drops approximately in half and + becomes much more readable.</li> +</ul> + <p>Possible problems:</p> +<ul> + <li>The combination of member function templates and implicit constructors can + result in unclear error messages when the user makes simple commonplace coding + errors. This should be much less of a problem with C++ concepts, but in the + meantime work continues to restrict over aggressive templates via enable_if/disable_if.</li> +</ul> + <h2><a name="Details">Details</a></h2> + +<table border="1" cellpadding="4" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" width="100%"> + <tr> + <td width="33%" colspan="3"> + <p align="center"><b><i>Encoding </i></b><i><b>Conversions</b></i></td> + </tr> + <tr> + <td width="33%"> + <p align="center"><i><b>Host system</b></i></td> + <td width="33%"> + <p align="center"><i><b>char string path arguments</b></i></td> + <td width="34%"> + <p align="center"><i><b>wide string path arguments</b></i></td> + </tr> + <tr> + <td width="33%">Systems with <code>char</code> as the native API path character type (i.e. + POSIX-like systems)</td> + <td width="33%">No conversion.</td> + <td width="34%">Conversion occurs, performed by the current path locale's + <code>codecvt</code> facet.</td> + </tr> + <tr> + <td width="33%">Systems with <code>wchar_t</code> as the native API path character type + (i.e. Windows-like systems).</td> + <td width="33%">Conversion occurs, performed by the current path locale's + <code>codecvt</code> facet.</td> + <td width="34%">No conversion.</td> + </tr> +</table> + +<p>When a class path function argument type matches the the operating system's +API argument type for paths, no conversion is performed rather than conversion +to a specified encoding such as one of the Unicode encodings. This avoids +unintended consequences, etc.</p> + +<h2><a name="Other-changes">Other changes</a></h2> + +<p><b>Uniform hybrid error handling: </b>The hybrid error handling idiom has +been consistently applied to all applicable functions.</p> + +<h2><a name="Acknowledgements">Acknowledgements</a></h2> + +<p>Peter Dimov suggested the idea of a single path class that could cope with +multiple character types and encodings. Walter Landry contributed both the design and implementation of the copy_any, +copy_directory, copy_symlink, and read_symlink functions.</p> + +<hr> +<p>Revised +<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->20 February, 2011<!--webbot bot="Timestamp" endspan i-checksum="40524" --></p> + +<p>© Copyright Beman Dawes, 2008</p> +<p> Use, modification, and distribution are subject to the Boost Software +License, Version 1.0. See <a href="http://www.boost.org/LICENSE_1_0.txt"> +www.boost.org/LICENSE_1_0.txt</a></p> + +</body> + +</html>
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