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href="#proj-rfc-3-dependency-management" title="Permalink to this headline">¶</a></h1> +<dl class="field-list simple"> +<dt class="field-odd">Author</dt> +<dd class="field-odd"><p>Kristian Evers</p> +</dd> +<dt class="field-even">Contact</dt> +<dd class="field-even"><p><a class="reference external" href="mailto:kreve%40sdfe.dk">kreve<span>@</span>sdfe<span>.</span>dk</a></p> +</dd> +<dt class="field-odd">Status</dt> +<dd class="field-odd"><p>Adopted</p> +</dd> +<dt class="field-even">Last Updated</dt> +<dd class="field-even"><p>2019-01-16</p> +</dd> +</dl> +<section id="summary"> +<h2>Summary<a class="headerlink" href="#summary" title="Permalink to this headline">¶</a></h2> +<p>This document defines a set of guidelines for dependency management in PROJ. +With PROJ being a core component in many downstream software packages clearly +stating which dependencies the library has is of great value. This document +concern both programming language standards as well as minimum required +versions of library dependencies and build tools.</p> +<p>It is proposed to adopt a rolling update scheme that ensures that PROJ is +sufficiently accessible, even on older systems, as well as keeping up with the +technological evolution. The scheme is divided in two parts, one concerning +versions of used programming languages within PROJ and the other concerning +software packages that PROJ depend on.</p> +<p>With adoption of this RFC, versions used for</p> +<ol class="arabic simple"> +<li><p>programming languages will always be at least two revisions behind the most +recent standard</p></li> +<li><p>software packages will always be at least two years old +(patch releases are exempt)</p></li> +</ol> +<p>A change in programming language standard can only be introduced with a new +major version release of PROJ. Changes for software package dependencies can be +introduced with minor version releases of PROJ. Changing the version +requirements for a dependency needs to be approved by the PSC.</p> +<p>Following the above rule set will ensure that all but the most conservative +users of PROJ will be able to build and use the most recent version of the +library.</p> +<p>In the sections below details concerning programming languages and software +dependencies are outlined. The RFC is concluded with a bootstrapping section +that details the state of dependencies after the accept of the RFC.</p> +</section> +<section id="background"> +<h2>Background<a class="headerlink" href="#background" title="Permalink to this headline">¶</a></h2> +<p>PROJ has traditionally been written in C89. Until recently, no formal +requirements of e.g. build systems has been defined and formally accepted by +the project. <a class="reference internal" href="rfc-2.html#rfc2"><span class="std std-ref">RFC2</span></a> formally introduces dependencies on C++11 and +SQLite 3.7.</p> +<p>In this RFC a rolling update of version or standard requirements is described. +The reasoning behind a rolling update scheme is that it has become increasingly +evident that C89 is becoming outdated and creating a less than optimal +development environment for contributors. It has been noted that the most +commonly used compilers all now support more recent versions of C, so the +strict usage of C89 is no longer as critical as it used to be.</p> +<p>Similarly, rolling updates to other tools and libraries that PROJ depend on +will ensure that the code base can be kept modern and in line with the rest of +the open source software ecosphere.</p> +</section> +<section id="c-and-c"> +<h2>C and C++<a class="headerlink" href="#c-and-c" title="Permalink to this headline">¶</a></h2> +<p>Following <a class="reference internal" href="rfc-2.html#rfc2"><span class="std std-ref">RFC2</span></a> PROJ is written in both C and C++. At the time of +writing the core library is C based and the code described in RFC2 is written +in C++. While the core library is mostly written in C it is compiled as C++. +Minor sections of PROJ, like the geodesic algorithms are still compiled as C +since there is no apparent benefit of compiling with a C++ compiler. This may +change in the future.</p> +<p>Both the C and C++ standards are updated with regular intervals. After an +update of a standard it takes time for compiler manufacturers to implement the +standards fully, which makes adaption of new standards potentially troublesome +if done too soon. On the other hand, waiting too long to adopt new standards +will eventually make the code base feel old and new contributors are more +likely to stay away because they don’t want to work using tools of the past. +With a rolling update scheme both concerns can be managed by always staying +behind the most recent standard, but not so far away that potential +contributors are scared away. Keeping a policy of always lagging behind be two +iterations of the standard is thought to be the best comprise between the two +concerns.</p> +<p>C comes in four ISO standardised varieties: C89, C99, C11, C18. In this +document we refer to their informal names for ease of reading. C++ exists in +five varieties: C++98, C++03, C++11, C++14, C++17. Before adoption of this RFC +PROJ uses C89 and C++11. For C, that means that the used standard is three +iterations behind the most recent standard. C++ is two iterations behind. +Following the rules in this RFC the required C standard used in PROJ is at +allowed to be two iterations behind the most recent standard. That means that a +change to C99 is possible, as long as the PROJ PSC acknowledges such a change.</p> +<p>When a new standard for either C or C++ is released PROJ should consider +changing its requirement to the next standard in the line. For C++ that means a +change in standard roughly every three years, for C the periods between +standard updates is expected to be longer. Adaptation of new programming +language standards should be coordinated with a major version release of PROJ.</p> +</section> +<section id="software-dependencies"> +<h2>Software dependencies<a class="headerlink" href="#software-dependencies" title="Permalink to this headline">¶</a></h2> +<p>At the time of writing PROJ is dependent on very few external packages. In +fact only one runtime dependency is present: SQLite. Building PROJ also +requires one of two external dependencies for configuration: Autotools or +CMake.</p> +<p>As with programming language standards it is preferable that software +dependencies are a bit behind the most recent development. For this reason it +is required that the minimum version supported in PROJ dependencies is at least +two years old, preferably more. It is not a requirement that the minimum +version of dependencies is always kept strictly two years behind current +development, but it is allowed in case future development of PROJ warrants an +update. Changes in minimum version requirements are allowed to happen with +minor version releases of PROJ.</p> +<p>At the time of writing the minimum version required for SQLite it 3.7 which was +released in 2010. CMake currently is required to be at least at version 2.8.3 +which was also released in 2010.</p> +</section> +<section id="bootstrapping"> +<h2>Bootstrapping<a class="headerlink" href="#bootstrapping" title="Permalink to this headline">¶</a></h2> +<p>This RFC comes with a set of guidelines for handling dependencies for PROJ in +the future. Up until now dependencies hasn’t been handled consistently, with +some dependencies not being approved formally by the projects governing body. +Therefore minimum versions of PROJ dependencies is proposed so that at the +acception of this RFC PROJ will have the following external requirements:</p> +<ul class="simple"> +<li><p>C99 (was C89)</p></li> +<li><p>C++11 (already approved in <a class="reference internal" href="rfc-2.html#rfc2"><span class="std std-ref">RFC2</span></a>)</p></li> +<li><p>SQLite 3.7 (already approved in <a class="reference internal" href="rfc-2.html#rfc2"><span class="std std-ref">RFC2</span></a>)</p></li> +<li><p>CMake 3.5 (was 2.8.3)</p></li> +</ul> +</section> +<section id="adoption-status"> +<h2>Adoption status<a class="headerlink" href="#adoption-status" title="Permalink to this headline">¶</a></h2> +<p>The RFC was adopted on 2018-01-19 with +1’s from the following PSC members</p> +<ul class="simple"> +<li><p>Kristian Evers</p></li> +<li><p>Even Rouault</p></li> +<li><p>Thomas Knudsen</p></li> +<li><p>Howard Butler</p></li> +</ul> +</section> +</section> + + + </div> + </div> + <footer><div class="rst-footer-buttons" role="navigation" aria-label="Footer"> + <a href="rfc-2.html" class="btn btn-neutral float-left" title="PROJ RFC 2: Initial integration of “GDAL SRS barn” work" accesskey="p" rel="prev"><span class="fa fa-arrow-circle-left" aria-hidden="true"></span> Previous</a> + <a href="rfc-4.html" class="btn btn-neutral float-right" title="PROJ RFC 4: Remote access to grids and GeoTIFF grids" accesskey="n" rel="next">Next <span class="fa fa-arrow-circle-right" aria-hidden="true"></span></a> + </div> + + <hr/> + + <div role="contentinfo"> + <p>© Copyright 1983-2022. + <span class="lastupdated">Last updated on 22 Mar 2022. + </span></p> + </div> + + Built with <a href="https://www.sphinx-doc.org/">Sphinx</a> using a + <a href="https://github.com/readthedocs/sphinx_rtd_theme">theme</a> + provided by <a href="https://readthedocs.org">Read the Docs</a>. + + +</footer> + </div> + </div> + </section> + </div> + <script> + jQuery(function () { + SphinxRtdTheme.Navigation.enable(true); + }); + </script> + +</body> +</html>
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