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| <div class="section" id="conventions"> |
| <h1>Conventions<a class="headerlink" href="#conventions" title="Permalink to this headline">¶</a></h1> |
| <p>This section provides some information about some of the abstractions and |
| development approaches we use to solve problems common to many parts of the C++ |
| project.</p> |
| <div class="section" id="file-naming"> |
| <h2>File Naming<a class="headerlink" href="#file-naming" title="Permalink to this headline">¶</a></h2> |
| <p>C++ source and header files should use underscores for word separation, not hyphens. |
| Compiled executables, however, will automatically use hyphens (such that |
| e.g. <code class="docutils literal notranslate"><span class="pre">src/arrow/scalar_test.cc</span></code> will be compiled into <code class="docutils literal notranslate"><span class="pre">arrow-scalar-test</span></code>).</p> |
| <p>C++ header files use the <code class="docutils literal notranslate"><span class="pre">.h</span></code> extension. Any header file name not |
| containing <code class="docutils literal notranslate"><span class="pre">internal</span></code> is considered to be a public header, and will be |
| automatically installed by the build.</p> |
| </div> |
| <div class="section" id="comments-and-docstrings"> |
| <h2>Comments and Docstrings<a class="headerlink" href="#comments-and-docstrings" title="Permalink to this headline">¶</a></h2> |
| <p>Regular comments start with <code class="docutils literal notranslate"><span class="pre">//</span></code>.</p> |
| <p>Doxygen docstrings start with <code class="docutils literal notranslate"><span class="pre">///</span></code>, and Doxygen directives start with <code class="docutils literal notranslate"><span class="pre">\</span></code>, |
| like this:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="c1">/// \brief Allocate a fixed size mutable buffer from a memory pool, zero its padding.</span> |
| <span class="c1">///</span> |
| <span class="c1">/// \param[in] size size of buffer to allocate</span> |
| <span class="c1">/// \param[in] pool a memory pool</span> |
| <span class="n">ARROW_EXPORT</span> |
| <span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">unique_ptr</span><span class="o"><</span><span class="n">Buffer</span><span class="o">>></span> <span class="n">AllocateBuffer</span><span class="p">(</span><span class="k">const</span> <span class="kt">int64_t</span> <span class="n">size</span><span class="p">,</span> |
| <span class="n">MemoryPool</span><span class="o">*</span> <span class="n">pool</span> <span class="o">=</span> <span class="n">NULLPTR</span><span class="p">);</span> |
| </pre></div> |
| </div> |
| <p>The summary line of a docstring uses the infinitive, not the indicative |
| (for example, “Allocate a buffer” rather than “Allocates a buffer”).</p> |
| </div> |
| <div class="section" id="memory-pools"> |
| <h2>Memory Pools<a class="headerlink" href="#memory-pools" title="Permalink to this headline">¶</a></h2> |
| <p>We provide a default memory pool with <code class="docutils literal notranslate"><span class="pre">arrow::default_memory_pool()</span></code>.</p> |
| </div> |
| <div class="section" id="error-handling-and-exceptions"> |
| <h2>Error Handling and Exceptions<a class="headerlink" href="#error-handling-and-exceptions" title="Permalink to this headline">¶</a></h2> |
| <p>For error handling, we return <code class="docutils literal notranslate"><span class="pre">arrow::Status</span></code> values instead of throwing C++ |
| exceptions. Since the Arrow C++ libraries are intended to be useful as a |
| component in larger C++ projects, using <code class="docutils literal notranslate"><span class="pre">Status</span></code> objects can help with good |
| code hygiene by making explicit when a function is expected to be able to fail.</p> |
| <p>A more recent option is to return a <code class="docutils literal notranslate"><span class="pre">arrow::Result<T></span></code> object that can |
| represent either a successful result with a <code class="docutils literal notranslate"><span class="pre">T</span></code> value, or an error result |
| with a <code class="docutils literal notranslate"><span class="pre">Status</span></code> value.</p> |
| <p>For expressing internal invariants and “cannot fail” errors, we use <code class="docutils literal notranslate"><span class="pre">DCHECK</span></code> macros |
| defined in <code class="docutils literal notranslate"><span class="pre">arrow/util/logging.h</span></code>. These checks are disabled in release builds |
| and are intended to catch internal development errors, particularly when |
| refactoring. These macros are not to be included in any public header files.</p> |
| <p>Since we do not use exceptions, we avoid doing expensive work in object |
| constructors. Objects that are expensive to construct may often have private |
| constructors, with public static factory methods that return <code class="docutils literal notranslate"><span class="pre">Status</span></code> or |
| <code class="docutils literal notranslate"><span class="pre">Result<T></span></code>.</p> |
| <p>There are a number of object constructors, like <code class="docutils literal notranslate"><span class="pre">arrow::Schema</span></code> and |
| <code class="docutils literal notranslate"><span class="pre">arrow::RecordBatch</span></code> where larger STL container objects like <code class="docutils literal notranslate"><span class="pre">std::vector</span></code> may |
| be created. While it is possible for <code class="docutils literal notranslate"><span class="pre">std::bad_alloc</span></code> to be thrown in these |
| constructors, the circumstances where they would are somewhat esoteric, and it |
| is likely that an application would have encountered other more serious |
| problems prior to having <code class="docutils literal notranslate"><span class="pre">std::bad_alloc</span></code> thrown in a constructor.</p> |
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