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138 lines
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<!-- This manual documents Guile version 3.0.10.
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Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
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Inc.
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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Permission is granted to copy, distribute and/or modify this document
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<title>Accessing Heap Object Fields (Guile Reference Manual)</title>
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="The-SCM-Type-in-Guile.html" rel="up" title="The SCM Type in Guile">
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<div class="subsubsection-level-extent" id="Accessing-Heap-Object-Fields">
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<p>
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Previous: <a href="Heap-Object-Type-Information.html" accesskey="p" rel="prev">Heap Object Type Information</a>, Up: <a href="The-SCM-Type-in-Guile.html" accesskey="u" rel="up">The SCM Type in Guile</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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<hr>
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<h4 class="subsubsection" id="Accessing-Heap-Object-Fields-1"><span>9.2.5.6 Accessing Heap Object Fields<a class="copiable-link" href="#Accessing-Heap-Object-Fields-1"> ¶</a></span></h4>
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<p>For a non-immediate Scheme object <var class="var">x</var>, the object type can be
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determined by using the <code class="code">SCM_CELL_TYPE</code> macro described in the
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previous section. For each different type of heap object it is known
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which fields hold tagged Scheme objects and which fields hold untagged
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raw data. To access the different fields appropriately, the following
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macros are provided.
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</p>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-SCM_005fCELL_005fWORD"><span class="category-def">Macro: </span><span><code class="def-type">scm_t_bits</code> <strong class="def-name">SCM_CELL_WORD</strong> <code class="def-code-arguments">(SCM <var class="var">x</var>, unsigned int <var class="var">n</var>)</code><a class="copiable-link" href="#index-SCM_005fCELL_005fWORD"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-SCM_005fCELL_005fWORD_005f0"><span class="category-def">Macro: </span><span><code class="def-type">scm_t_bits</code> <strong class="def-name">SCM_CELL_WORD_0</strong> <code class="def-code-arguments">(<var class="var">x</var>)</code><a class="copiable-link" href="#index-SCM_005fCELL_005fWORD_005f0"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-SCM_005fCELL_005fWORD_005f1"><span class="category-def">Macro: </span><span><code class="def-type">scm_t_bits</code> <strong class="def-name">SCM_CELL_WORD_1</strong> <code class="def-code-arguments">(<var class="var">x</var>)</code><a class="copiable-link" href="#index-SCM_005fCELL_005fWORD_005f1"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-SCM_005fCELL_005fWORD_005f2"><span class="category-def">Macro: </span><span><code class="def-type">scm_t_bits</code> <strong class="def-name">SCM_CELL_WORD_2</strong> <code class="def-code-arguments">(<var class="var">x</var>)</code><a class="copiable-link" href="#index-SCM_005fCELL_005fWORD_005f2"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-SCM_005fCELL_005fWORD_005f3"><span class="category-def">Macro: </span><span><code class="def-type">scm_t_bits</code> <strong class="def-name">SCM_CELL_WORD_3</strong> <code class="def-code-arguments">(<var class="var">x</var>)</code><a class="copiable-link" href="#index-SCM_005fCELL_005fWORD_005f3"> ¶</a></span></dt>
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<dd><p>Deliver the field <var class="var">n</var> of the heap object referenced by the
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non-immediate Scheme object <var class="var">x</var> as raw untagged data. Only use this
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macro for fields containing untagged data; don’t use it for fields
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containing tagged <code class="code">SCM</code> objects.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-SCM_005fCELL_005fOBJECT"><span class="category-def">Macro: </span><span><code class="def-type">SCM</code> <strong class="def-name">SCM_CELL_OBJECT</strong> <code class="def-code-arguments">(SCM <var class="var">x</var>, unsigned int <var class="var">n</var>)</code><a class="copiable-link" href="#index-SCM_005fCELL_005fOBJECT"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-SCM_005fCELL_005fOBJECT_005f0"><span class="category-def">Macro: </span><span><code class="def-type">SCM</code> <strong class="def-name">SCM_CELL_OBJECT_0</strong> <code class="def-code-arguments">(SCM <var class="var">x</var>)</code><a class="copiable-link" href="#index-SCM_005fCELL_005fOBJECT_005f0"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-SCM_005fCELL_005fOBJECT_005f1"><span class="category-def">Macro: </span><span><code class="def-type">SCM</code> <strong class="def-name">SCM_CELL_OBJECT_1</strong> <code class="def-code-arguments">(SCM <var class="var">x</var>)</code><a class="copiable-link" href="#index-SCM_005fCELL_005fOBJECT_005f1"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-SCM_005fCELL_005fOBJECT_005f2"><span class="category-def">Macro: </span><span><code class="def-type">SCM</code> <strong class="def-name">SCM_CELL_OBJECT_2</strong> <code class="def-code-arguments">(SCM <var class="var">x</var>)</code><a class="copiable-link" href="#index-SCM_005fCELL_005fOBJECT_005f2"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-SCM_005fCELL_005fOBJECT_005f3"><span class="category-def">Macro: </span><span><code class="def-type">SCM</code> <strong class="def-name">SCM_CELL_OBJECT_3</strong> <code class="def-code-arguments">(SCM <var class="var">x</var>)</code><a class="copiable-link" href="#index-SCM_005fCELL_005fOBJECT_005f3"> ¶</a></span></dt>
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<dd><p>Deliver the field <var class="var">n</var> of the heap object referenced by the
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non-immediate Scheme object <var class="var">x</var> as a Scheme object. Only use this
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macro for fields containing tagged <code class="code">SCM</code> objects; don’t use it for
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fields containing untagged data.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-SCM_005fSET_005fCELL_005fWORD"><span class="category-def">Macro: </span><span><code class="def-type">void</code> <strong class="def-name">SCM_SET_CELL_WORD</strong> <code class="def-code-arguments">(SCM <var class="var">x</var>, unsigned int <var class="var">n</var>, scm_t_bits <var class="var">w</var>)</code><a class="copiable-link" href="#index-SCM_005fSET_005fCELL_005fWORD"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-SCM_005fSET_005fCELL_005fWORD_005f0"><span class="category-def">Macro: </span><span><code class="def-type">void</code> <strong class="def-name">SCM_SET_CELL_WORD_0</strong> <code class="def-code-arguments">(<var class="var">x</var>, <var class="var">w</var>)</code><a class="copiable-link" href="#index-SCM_005fSET_005fCELL_005fWORD_005f0"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-SCM_005fSET_005fCELL_005fWORD_005f1"><span class="category-def">Macro: </span><span><code class="def-type">void</code> <strong class="def-name">SCM_SET_CELL_WORD_1</strong> <code class="def-code-arguments">(<var class="var">x</var>, <var class="var">w</var>)</code><a class="copiable-link" href="#index-SCM_005fSET_005fCELL_005fWORD_005f1"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-SCM_005fSET_005fCELL_005fWORD_005f2"><span class="category-def">Macro: </span><span><code class="def-type">void</code> <strong class="def-name">SCM_SET_CELL_WORD_2</strong> <code class="def-code-arguments">(<var class="var">x</var>, <var class="var">w</var>)</code><a class="copiable-link" href="#index-SCM_005fSET_005fCELL_005fWORD_005f2"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-SCM_005fSET_005fCELL_005fWORD_005f3"><span class="category-def">Macro: </span><span><code class="def-type">void</code> <strong class="def-name">SCM_SET_CELL_WORD_3</strong> <code class="def-code-arguments">(<var class="var">x</var>, <var class="var">w</var>)</code><a class="copiable-link" href="#index-SCM_005fSET_005fCELL_005fWORD_005f3"> ¶</a></span></dt>
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<dd><p>Write the raw value <var class="var">w</var> into field number <var class="var">n</var> of the heap object
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referenced by the non-immediate Scheme value <var class="var">x</var>. Values that are
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written into heap objects as raw values should only be read later using
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the <code class="code">SCM_CELL_WORD</code> macros.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-SCM_005fSET_005fCELL_005fOBJECT"><span class="category-def">Macro: </span><span><code class="def-type">void</code> <strong class="def-name">SCM_SET_CELL_OBJECT</strong> <code class="def-code-arguments">(SCM <var class="var">x</var>, unsigned int <var class="var">n</var>, SCM <var class="var">o</var>)</code><a class="copiable-link" href="#index-SCM_005fSET_005fCELL_005fOBJECT"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-SCM_005fSET_005fCELL_005fOBJECT_005f0"><span class="category-def">Macro: </span><span><code class="def-type">void</code> <strong class="def-name">SCM_SET_CELL_OBJECT_0</strong> <code class="def-code-arguments">(SCM <var class="var">x</var>, SCM <var class="var">o</var>)</code><a class="copiable-link" href="#index-SCM_005fSET_005fCELL_005fOBJECT_005f0"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-SCM_005fSET_005fCELL_005fOBJECT_005f1"><span class="category-def">Macro: </span><span><code class="def-type">void</code> <strong class="def-name">SCM_SET_CELL_OBJECT_1</strong> <code class="def-code-arguments">(SCM <var class="var">x</var>, SCM <var class="var">o</var>)</code><a class="copiable-link" href="#index-SCM_005fSET_005fCELL_005fOBJECT_005f1"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-SCM_005fSET_005fCELL_005fOBJECT_005f2"><span class="category-def">Macro: </span><span><code class="def-type">void</code> <strong class="def-name">SCM_SET_CELL_OBJECT_2</strong> <code class="def-code-arguments">(SCM <var class="var">x</var>, SCM <var class="var">o</var>)</code><a class="copiable-link" href="#index-SCM_005fSET_005fCELL_005fOBJECT_005f2"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-SCM_005fSET_005fCELL_005fOBJECT_005f3"><span class="category-def">Macro: </span><span><code class="def-type">void</code> <strong class="def-name">SCM_SET_CELL_OBJECT_3</strong> <code class="def-code-arguments">(SCM <var class="var">x</var>, SCM <var class="var">o</var>)</code><a class="copiable-link" href="#index-SCM_005fSET_005fCELL_005fOBJECT_005f3"> ¶</a></span></dt>
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<dd><p>Write the Scheme object <var class="var">o</var> into field number <var class="var">n</var> of the heap
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object referenced by the non-immediate Scheme value <var class="var">x</var>. Values
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that are written into heap objects as objects should only be read using
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the <code class="code">SCM_CELL_OBJECT</code> macros.
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</p></dd></dl>
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<p>Summary:
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</p><ul class="itemize mark-bullet">
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<li>For a non-immediate Scheme object <var class="var">x</var> of unknown type, get the type
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information by using <code class="code">SCM_CELL_TYPE (<var class="var">x</var>)</code>.
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</li><li>As soon as the type information is available, only use the appropriate
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access methods to read and write data to the different heap object
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fields.
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</li><li>Note that field 0 stores the cell type information. Generally speaking,
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other data associated with a heap object is stored starting from field
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1.
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</li></ul>
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</div>
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<hr>
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<div class="nav-panel">
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<p>
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Previous: <a href="Heap-Object-Type-Information.html">Heap Object Type Information</a>, Up: <a href="The-SCM-Type-in-Guile.html">The SCM Type in Guile</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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