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  1. <!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="API documentation for the Rust `buffer` mod in crate `syn`."><meta name="keywords" content="rust, rustlang, rust-lang, buffer"><title>syn::buffer - Rust</title><link rel="stylesheet" type="text/css" href="../../normalize.css"><link rel="stylesheet" type="text/css" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../dark.css"><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><script src="../../storage.js"></script></head><body class="rustdoc mod"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">&#9776;</div><p class='location'>Module buffer</p><div class="sidebar-elems"><div class="block items"><ul><li><a href="#structs">Structs</a></li></ul></div><p class='location'><a href='../index.html'>syn</a></p><script>window.sidebarCurrent = {name: 'buffer', ty: 'mod', relpath: '../'};</script><script defer src="../sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../theme.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><input class="search-input" name="search" autocomplete="off" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><a id="settings-menu" href="../../settings.html"><img src="../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='in-band'>Module <a href='../index.html'>syn</a>::<wbr><a class="mod" href=''>buffer</a></span><span class='out-of-band'><span id='render-detail'><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class='inner'>&#x2212;</span>]</a></span><a class='srclink' href='../../src/syn/buffer.rs.html#9-469' title='goto source code'>[src]</a></span></h1><div class='docblock'><p>A stably addressed token buffer supporting efficient traversal based on a
    2. 

  2. cheaply copyable cursor.</p>
    3. 

  3. <p>The <a href="../synom/trait.Synom.html"><code>Synom</code></a> trait is implemented for syntax tree types that can be parsed
    4. 

  4. from one of these token cursors.</p>
    5. 

  5. <p><em>This module is available if Syn is built with the <code>&quot;parsing&quot;</code> feature.</em></p>
    6. 

  6. <h1 id="example" class="section-header"><a href="#example">Example</a></h1>
    7. 

  7. <p>This example shows a basic token parser for parsing a token stream without
    8. 

  8. using Syn's parser combinator macros.</p>
    9. 

  9. 

  10. <pre class="rust rust-example-rendered">
    11. 

  11. <span class="attribute">#![<span class="ident">feature</span>(<span class="ident">proc_macro_diagnostic</span>)]</span>
    12. 

  12. 

  13. <span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">syn</span>;
    14. 

  14. <span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">proc_macro</span>;
    15. 

  15. 

  16. <span class="attribute">#[<span class="ident">macro_use</span>]</span>
    17. 

  17. <span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">quote</span>;
    18. 

  18. 

  19. <span class="kw">use</span> <span class="ident">syn</span>::{<span class="ident">token</span>, <span class="ident">ExprTuple</span>};
    20. 

  20. <span class="kw">use</span> <span class="ident">syn</span>::<span class="ident">buffer</span>::{<span class="ident">Cursor</span>, <span class="ident">TokenBuffer</span>};
    21. 

  21. <span class="kw">use</span> <span class="ident">syn</span>::<span class="ident">spanned</span>::<span class="ident">Spanned</span>;
    22. 

  22. <span class="kw">use</span> <span class="ident">syn</span>::<span class="ident">synom</span>::<span class="ident">Synom</span>;
    23. 

  23. <span class="kw">use</span> <span class="ident">proc_macro</span>::{<span class="ident">Diagnostic</span>, <span class="ident">Span</span>, <span class="ident">TokenStream</span>};
    24. 

  24. 

  25. <span class="doccomment">/// A basic token parser for parsing a token stream without using Syn&#39;s</span>
    26. 

  26. <span class="doccomment">/// parser combinator macros.</span>
    27. 

  27. <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Parser</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span> {
    28. 

  28.     <span class="ident">cursor</span>: <span class="ident">Cursor</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span>,
    29. 

  29. }
    30. 

  30. 

  31. <span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span> <span class="ident">Parser</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span> {
    32. 

  32.     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">cursor</span>: <span class="ident">Cursor</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span>) <span class="op">-&gt;</span> <span class="self">Self</span> {
    33. 

  33.         <span class="ident">Parser</span> { <span class="ident">cursor</span> }
    34. 

  34.     }
    35. 

  35. 

  36.     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">current_span</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">Span</span> {
    37. 

  37.         <span class="self">self</span>.<span class="ident">cursor</span>.<span class="ident">span</span>().<span class="ident">unstable</span>()
    38. 

  38.     }
    39. 

  39. 

  40.     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">parse</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="ident">Synom</span><span class="op">&gt;</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Result</span><span class="op">&lt;</span><span class="ident">T</span>, <span class="ident">Diagnostic</span><span class="op">&gt;</span> {
    41. 

  41.         <span class="kw">let</span> (<span class="ident">val</span>, <span class="ident">rest</span>) <span class="op">=</span> <span class="ident">T</span>::<span class="ident">parse</span>(<span class="self">self</span>.<span class="ident">cursor</span>)
    42. 

  42.             .<span class="ident">map_err</span>(<span class="op">|</span><span class="ident">e</span><span class="op">|</span> <span class="kw">match</span> <span class="ident">T</span>::<span class="ident">description</span>() {
    43. 

  43.                 <span class="prelude-val">Some</span>(<span class="ident">desc</span>) <span class="op">=&gt;</span> {
    44. 

  44.                     <span class="self">self</span>.<span class="ident">current_span</span>().<span class="ident">error</span>(<span class="macro">format</span><span class="macro">!</span>(<span class="string">&quot;{}: expected {}&quot;</span>, <span class="ident">e</span>, <span class="ident">desc</span>))
    45. 

  45.                 }
    46. 

  46.                 <span class="prelude-val">None</span> <span class="op">=&gt;</span> {
    47. 

  47.                     <span class="self">self</span>.<span class="ident">current_span</span>().<span class="ident">error</span>(<span class="ident">e</span>.<span class="ident">to_string</span>())
    48. 

  48.                 }
    49. 

  49.             })<span class="question-mark">?</span>;
    50. 

  50. 

  51.         <span class="self">self</span>.<span class="ident">cursor</span> <span class="op">=</span> <span class="ident">rest</span>;
    52. 

  52.         <span class="prelude-val">Ok</span>(<span class="ident">val</span>)
    53. 

  53.     }
    54. 

  54. 

  55.     <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">expect_eof</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Result</span><span class="op">&lt;</span>(), <span class="ident">Diagnostic</span><span class="op">&gt;</span> {
    56. 

  56.         <span class="kw">if</span> <span class="op">!</span><span class="self">self</span>.<span class="ident">cursor</span>.<span class="ident">eof</span>() {
    57. 

  57.             <span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="self">self</span>.<span class="ident">current_span</span>().<span class="ident">error</span>(<span class="string">&quot;trailing characters; expected eof&quot;</span>));
    58. 

  58.         }
    59. 

  59. 

  60.         <span class="prelude-val">Ok</span>(())
    61. 

  61.     }
    62. 

  62. }
    63. 

  63. 

  64. <span class="kw">fn</span> <span class="ident">eval</span>(<span class="ident">input</span>: <span class="ident">TokenStream</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Result</span><span class="op">&lt;</span><span class="ident">TokenStream</span>, <span class="ident">Diagnostic</span><span class="op">&gt;</span> {
    65. 

  65.     <span class="kw">let</span> <span class="ident">buffer</span> <span class="op">=</span> <span class="ident">TokenBuffer</span>::<span class="ident">new</span>(<span class="ident">input</span>);
    66. 

  66.     <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">parser</span> <span class="op">=</span> <span class="ident">Parser</span>::<span class="ident">new</span>(<span class="ident">buffer</span>.<span class="ident">begin</span>());
    67. 

  67. 

  68.     <span class="comment">// Parse some syntax tree types out of the input tokens. In this case we</span>
    69. 

  69.     <span class="comment">// expect something like:</span>
    70. 

  70.     <span class="comment">//</span>
    71. 

  71.     <span class="comment">//     (a, b, c) = (1, 2, 3)</span>
    72. 

  72.     <span class="kw">let</span> <span class="ident">a</span> <span class="op">=</span> <span class="ident">parser</span>.<span class="ident">parse</span>::<span class="op">&lt;</span><span class="ident">ExprTuple</span><span class="op">&gt;</span>()<span class="question-mark">?</span>;
    73. 

  73.     <span class="ident">parser</span>.<span class="ident">parse</span>::<span class="op">&lt;</span><span class="ident">token</span>::<span class="ident">Eq</span><span class="op">&gt;</span>()<span class="question-mark">?</span>;
    74. 

  74.     <span class="kw">let</span> <span class="ident">b</span> <span class="op">=</span> <span class="ident">parser</span>.<span class="ident">parse</span>::<span class="op">&lt;</span><span class="ident">ExprTuple</span><span class="op">&gt;</span>()<span class="question-mark">?</span>;
    75. 

  75.     <span class="ident">parser</span>.<span class="ident">expect_eof</span>()<span class="question-mark">?</span>;
    76. 

  76. 

  77.     <span class="comment">// Perform some validation and report errors.</span>
    78. 

  78.     <span class="kw">let</span> (<span class="ident">a_len</span>, <span class="ident">b_len</span>) <span class="op">=</span> (<span class="ident">a</span>.<span class="ident">elems</span>.<span class="ident">len</span>(), <span class="ident">b</span>.<span class="ident">elems</span>.<span class="ident">len</span>());
    79. 

  79.     <span class="kw">if</span> <span class="ident">a_len</span> <span class="op">!=</span> <span class="ident">b_len</span> {
    80. 

  80.         <span class="kw">let</span> <span class="ident">diag</span> <span class="op">=</span> <span class="ident">b</span>.<span class="ident">span</span>().<span class="ident">unstable</span>()
    81. 

  81.             .<span class="ident">error</span>(<span class="macro">format</span><span class="macro">!</span>(<span class="string">&quot;expected {} element(s), got {}&quot;</span>, <span class="ident">a_len</span>, <span class="ident">b_len</span>))
    82. 

  82.             .<span class="ident">span_note</span>(<span class="ident">a</span>.<span class="ident">span</span>().<span class="ident">unstable</span>(), <span class="string">&quot;because of this&quot;</span>);
    83. 

  83. 

  84.         <span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="ident">diag</span>);
    85. 

  85.     }
    86. 

  86. 

  87.     <span class="comment">// Build the output tokens.</span>
    88. 

  88.     <span class="kw">let</span> <span class="ident">out</span> <span class="op">=</span> <span class="macro">quote</span><span class="macro">!</span> {
    89. 

  89.         <span class="macro">println</span><span class="macro">!</span>(<span class="string">&quot;All good! Received two tuples of size {}&quot;</span>, #<span class="ident">a_len</span>);
    90. 

  90.     };
    91. 

  91. 

  92.     <span class="prelude-val">Ok</span>(<span class="ident">out</span>.<span class="ident">into</span>())
    93. 

  93. }</pre>
    94. 

  94. </div><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
    95. 

  95. <table>
    96. 

  96.                        <tr class=' module-item'>
    97. 

  97.                            <td><a class="struct" href="struct.Cursor.html"
    98. 

  98.                                   title='struct syn::buffer::Cursor'>Cursor</a></td>
    99. 

  99.                            <td class='docblock-short'>
    100. 

  100.                                 <p>A cheaply copyable cursor into a <code>TokenBuffer</code>.</p>
    101. 

  101. 

  102.                            </td>
    103. 

  103.                        </tr>
    104. 

  104.                        <tr class=' module-item'>
    105. 

  105.                            <td><a class="struct" href="struct.TokenBuffer.html"
    106. 

  106.                                   title='struct syn::buffer::TokenBuffer'>TokenBuffer</a></td>
    107. 

  107.                            <td class='docblock-short'>
    108. 

  108.                                 <p>A buffer that can be efficiently traversed multiple times, unlike
    109. 

  109. <code>TokenStream</code> which requires a deep copy in order to traverse more than
    110. 

  110. once.</p>
    111. 

  111. 

  112.                            </td>
    113. 

  113.                        </tr></table></section><section id="search" class="content hidden"></section><section class="footer"></section><aside id="help" class="hidden"><div><h1 class="hidden">Help</h1><div class="shortcuts"><h2>Keyboard Shortcuts</h2><dl><dt><kbd>?</kbd></dt><dd>Show this help dialog</dd><dt><kbd>S</kbd></dt><dd>Focus the search field</dd><dt><kbd>↑</kbd></dt><dd>Move up in search results</dd><dt><kbd>↓</kbd></dt><dd>Move down in search results</dd><dt><kbd>↹</kbd></dt><dd>Switch tab</dd><dt><kbd>&#9166;</kbd></dt><dd>Go to active search result</dd><dt><kbd>+</kbd></dt><dd>Expand all sections</dd><dt><kbd>-</kbd></dt><dd>Collapse all sections</dd></dl></div><div class="infos"><h2>Search Tricks</h2><p>Prefix searches with a type followed by a colon (e.g. <code>fn:</code>) to restrict the search to a given type.</p><p>Accepted types are: <code>fn</code>, <code>mod</code>, <code>struct</code>, <code>enum</code>, <code>trait</code>, <code>type</code>, <code>macro</code>, and <code>const</code>.</p><p>Search functions by type signature (e.g. <code>vec -> usize</code> or <code>* -> vec</code>)</p><p>Search multiple things at once by splitting your query with comma (e.g. <code>str,u8</code> or <code>String,struct:Vec,test</code>)</p></div></div></aside><script>window.rootPath = "../../";window.currentCrate = "syn";</script><script src="../../aliases.js"></script><script src="../../main.js"></script><script defer src="../../search-index.js"></script></body></html>
    114.