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<div class="section" id="differences-between-d-yaml-and-the-yaml-specification">
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<h1>Differences between D:YAML and the YAML specification<a class="headerlink" href="#differences-between-d-yaml-and-the-yaml-specification" title="Permalink to this headline">¶</a></h1>
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<p>There are some differences between D:YAML and the YAML 1.1 specification. Some
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are caused by difficulty of implementation of some features, such as multiple
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Unicode encodings within single stream, and some by unnecessary restrictions or
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ambiguities in the specification.</p>
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<p>Still, D:YAML tries to be as close to the specification as possible. D:YAML should
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never load documents with different meaning than according to the specification,
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and documents that fail to load should be very rare (for instance, very few
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files use multiple Unicode encodings).</p>
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<div class="section" id="list-of-known-differences">
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<h2>List of known differences:<a class="headerlink" href="#list-of-known-differences" title="Permalink to this headline">¶</a></h2>
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<p>Differences that can cause valid YAML documents not to load:</p>
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<ul>
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<li><p class="first">At the moment, all mappings in the internal representation are ordered,
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and a comparison for equality between equal mappings with differing order
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will return false. This will be fixed once Phobos has a usable map type or
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D associative arrays work with variants.</p>
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</li>
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<li><p class="first">No support for byte order marks and multiple Unicode encodings in a stream.</p>
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</li>
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<li><p class="first">Plain scalars in flow context cannot contain <tt class="docutils literal"><span class="pre">,</span></tt>, <tt class="docutils literal"><span class="pre">:</span></tt> and <tt class="docutils literal"><span class="pre">?</span></tt>.
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This might change with <tt class="docutils literal"><span class="pre">:</span></tt> in the future.
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See <a class="reference external" href="http://pyyaml.org/wiki/YAMLColonInFlowContext">http://pyyaml.org/wiki/YAMLColonInFlowContext</a> for details.</p>
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</li>
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<li><p class="first">The specification does not restrict characters for anchors and
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aliases. This may lead to problems, for instance, the document:</p>
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<div class="highlight-yaml"><div class="highlight"><pre><span class="p-Indicator">[</span> <span class="nv">*alias</span><span class="p-Indicator">,</span> <span class="nv">value</span> <span class="p-Indicator">]</span>
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</pre></div>
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</div>
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<p>can be interpteted in two ways, as:</p>
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<div class="highlight-yaml"><div class="highlight"><pre><span class="p-Indicator">[</span> <span class="s">"value"</span> <span class="p-Indicator">]</span>
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</pre></div>
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</div>
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<p>and:</p>
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<div class="highlight-yaml"><div class="highlight"><pre><span class="p-Indicator">[</span> <span class="nv">*alias</span> <span class="p-Indicator">,</span> <span class="s">"value"</span> <span class="p-Indicator">]</span>
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</pre></div>
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</div>
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<p>Therefore we restrict aliases and anchors to ASCII alphanumeric characters.</p>
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</li>
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<li><p class="first">The specification is confusing about tabs in plain scalars. We don’t use tabs
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in plain scalars at all.</p>
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</li>
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<li><p class="first">There is no support for recursive data structures in DYAML.</p>
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</li>
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</ul>
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<p>Other differences:</p>
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<ul>
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<li><p class="first">Indentation is ignored in the flow context, which is less restrictive than the
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specification. This allows code such as:</p>
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<div class="highlight-yaml"><div class="highlight"><pre><span class="l-Scalar-Plain">key</span><span class="p-Indicator">:</span> <span class="p-Indicator">{</span>
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<span class="p-Indicator">}</span>
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</pre></div>
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</div>
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</li>
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<li><p class="first">Indentation rules for quoted scalars are loosed: They don’t need to adhere
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indentation as <tt class="docutils literal"><span class="pre">"</span></tt> and <tt class="docutils literal"><span class="pre">'</span></tt> clearly mark the beginning and the end of them.</p>
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</li>
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<li><p class="first">We allow <tt class="docutils literal"><span class="pre">_</span></tt> in tag handles.</p>
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</li>
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<li><p class="first">Right now, two mappings with the same contents but different orderings are
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considered unequal, even if they are unordered mappings. This is because all
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mappings are ordered in the D:YAML implementation. This should change in
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future, once D associative arrays work with variant types or a map class or
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struct appears in Phobos.</p>
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</li>
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</ul>
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<h3><a href="../index.html">Table Of Contents</a></h3>
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<ul>
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<li><a class="reference internal" href="#">Differences between D:YAML and the YAML specification</a><ul>
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<li><a class="reference internal" href="#list-of-known-differences">List of known differences:</a></li>
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</ul>
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</li>
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>previous</a></li>
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© Copyright 2011, Ferdinand Majerech. Based on PyYAML http://www.pyyaml.org by Kirill Simonov.
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Last updated on Aug 16, 2011.
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