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rippled/md_ripple_protocol_README.html
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<div class="title">protocol </div> </div>
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<div class="textblock"><p>Classes and functions for handling data and values associated with the XRP Ledger protocol.</p>
<h1><a class="anchor" id="autotoc_md270"></a>
Serialized Objects</h1>
<p>Objects transmitted over the network must be serialized into a canonical format. The prefix "ST" refers to classes that deal with the serialized format.</p>
<p>The term "Tx" or "tx" is an abbreviation for "Transaction", a commonly occurring object type.</p>
<h2><a class="anchor" id="autotoc_md271"></a>
Optional Fields</h2>
<p>Our serialized fields have some "type magic" to make optional fields easier to read:</p>
<ul>
<li>The operation <code>x[sfFoo]</code> means "return the value of 'Foo'
if it exists, or the default value if it doesn't."</li>
<li>The operation <code>x[~sfFoo]</code> means "return the value of 'Foo'
if it exists, or nothing if it doesn't." This usage of the tilde/bitwise NOT operator is not standard outside of the <code>rippled</code> codebase.<ul>
<li>As a consequence of this, <code>x[~sfFoo] = y[~sfFoo]</code> assigns the value of Foo from y to x, including omitting Foo from x if it doesn't exist in y.</li>
</ul>
</li>
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<p>Typically, for things that are guaranteed to exist, you use <code>x[sfFoo]</code> and avoid having to deal with a container that may or may not hold a value. For things not guaranteed to exist, you use <code>x[~sfFoo]</code> because you want such a container. It avoids having to look something up twice, once just to see if it exists and a second time to get/set its value. (<a href="https://github.com/ripple/rippled/blob/35f4698aed5dce02f771b34cfbb690495cb5efcc/src/ripple/app/tx/impl/PayChan.cpp#L229-L236">Real example</a>)</p>
<p>The source of this "type magic" is in <a href="./SField.h#L296-L302">SField.h</a>.</p>
<h2><a class="anchor" id="autotoc_md272"></a>
Related Resources</h2>
<ul>
<li><a href="https://github.com/XRPLF/xrpl.js/tree/main/packages/ripple-binary-codec/src/enums">ripple-binary-codec SField enums</a></li>
<li><a href="https://github.com/XRPLF/sFieldRegistry">SFCode Registry Tables</a> </li>
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