<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <link rel="stylesheet" href="style.css" type="text/css"> <meta content="text/html; charset=iso-8859-1" http-equiv="Content-Type"> <link rel="Start" href="index.html"> <link rel="previous" href="GraphicsX11.html"> <link rel="next" href="Int32.html"> <link rel="Up" href="index.html"> <link title="Index of types" rel=Appendix href="index_types.html"> <link title="Index of exceptions" rel=Appendix href="index_exceptions.html"> <link title="Index of values" rel=Appendix href="index_values.html"> <link title="Index of modules" rel=Appendix href="index_modules.html"> <link title="Index of module types" rel=Appendix href="index_module_types.html"> <link title="Arg" rel="Chapter" href="Arg.html"> <link title="Arith_status" rel="Chapter" href="Arith_status.html"> <link title="Array" rel="Chapter" href="Array.html"> <link title="ArrayLabels" rel="Chapter" href="ArrayLabels.html"> <link title="Big_int" rel="Chapter" 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href="Tk.html"> <link title="Unix" rel="Chapter" href="Unix.html"> <link title="UnixLabels" rel="Chapter" href="UnixLabels.html"> <link title="Weak" rel="Chapter" href="Weak.html"><link title="Generic interface" rel="Section" href="#6_Genericinterface"> <link title="Functorial interface" rel="Section" href="#6_Functorialinterface"> <link title="The polymorphic hash primitive" rel="Section" href="#6_Thepolymorphichashprimitive"> <title>Hashtbl</title> </head> <body> <div class="navbar"><a href="GraphicsX11.html">Previous</a> <a href="index.html">Up</a> <a href="Int32.html">Next</a> </div> <center><h1>Module <a href="type_Hashtbl.html">Hashtbl</a></h1></center> <br> <pre><span class="keyword">module</span> Hashtbl: <code class="code"><span class="keyword">sig</span></code> <a href="Hashtbl.html">..</a> <code class="code"><span class="keyword">end</span></code></pre>Hash tables and hash functions. <p> Hash tables are hashed association tables, with in-place modification.<br> <hr width="100%"> <br> <span id="6_Genericinterface"><h6>Generic interface</h6></span><br> <pre><span id="TYPEt"><span class="keyword">type</span> <code class="type">('a, 'b)</code> t</span> </pre> <div class="info"> The type of hash tables from type <code class="code"><span class="keywordsign">'</span>a</code> to type <code class="code"><span class="keywordsign">'</span>b</code>.<br> </div> <pre><span id="VALcreate"><span class="keyword">val</span> create</span> : <code class="type">int -> ('a, 'b) <a href="Hashtbl.html#TYPEt">t</a></code></pre><div class="info"> <code class="code"><span class="constructor">Hashtbl</span>.create n</code> creates a new, empty hash table, with initial size <code class="code">n</code>. For best results, <code class="code">n</code> should be on the order of the expected number of elements that will be in the table. The table grows as needed, so <code class="code">n</code> is just an initial guess.<br> </div> <pre><span id="VALclear"><span class="keyword">val</span> clear</span> : <code class="type">('a, 'b) <a href="Hashtbl.html#TYPEt">t</a> -> unit</code></pre><div class="info"> Empty a hash table.<br> </div> <pre><span id="VALadd"><span class="keyword">val</span> add</span> : <code class="type">('a, 'b) <a href="Hashtbl.html#TYPEt">t</a> -> 'a -> 'b -> unit</code></pre><div class="info"> <code class="code"><span class="constructor">Hashtbl</span>.add tbl x y</code> adds a binding of <code class="code">x</code> to <code class="code">y</code> in table <code class="code">tbl</code>. Previous bindings for <code class="code">x</code> are not removed, but simply hidden. That is, after performing <a href="Hashtbl.html#VALremove"><code class="code"><span class="constructor">Hashtbl</span>.remove</code></a><code class="code"> tbl x</code>, the previous binding for <code class="code">x</code>, if any, is restored. (Same behavior as with association lists.)<br> </div> <pre><span id="VALcopy"><span class="keyword">val</span> copy</span> : <code class="type">('a, 'b) <a href="Hashtbl.html#TYPEt">t</a> -> ('a, 'b) <a href="Hashtbl.html#TYPEt">t</a></code></pre><div class="info"> Return a copy of the given hashtable.<br> </div> <pre><span id="VALfind"><span class="keyword">val</span> find</span> : <code class="type">('a, 'b) <a href="Hashtbl.html#TYPEt">t</a> -> 'a -> 'b</code></pre><div class="info"> <code class="code"><span class="constructor">Hashtbl</span>.find tbl x</code> returns the current binding of <code class="code">x</code> in <code class="code">tbl</code>, or raises <code class="code"><span class="constructor">Not_found</span></code> if no such binding exists.<br> </div> <pre><span id="VALfind_all"><span class="keyword">val</span> find_all</span> : <code class="type">('a, 'b) <a href="Hashtbl.html#TYPEt">t</a> -> 'a -> 'b list</code></pre><div class="info"> <code class="code"><span class="constructor">Hashtbl</span>.find_all tbl x</code> returns the list of all data associated with <code class="code">x</code> in <code class="code">tbl</code>. The current binding is returned first, then the previous bindings, in reverse order of introduction in the table.<br> </div> <pre><span id="VALmem"><span class="keyword">val</span> mem</span> : <code class="type">('a, 'b) <a href="Hashtbl.html#TYPEt">t</a> -> 'a -> bool</code></pre><div class="info"> <code class="code"><span class="constructor">Hashtbl</span>.mem tbl x</code> checks if <code class="code">x</code> is bound in <code class="code">tbl</code>.<br> </div> <pre><span id="VALremove"><span class="keyword">val</span> remove</span> : <code class="type">('a, 'b) <a href="Hashtbl.html#TYPEt">t</a> -> 'a -> unit</code></pre><div class="info"> <code class="code"><span class="constructor">Hashtbl</span>.remove tbl x</code> removes the current binding of <code class="code">x</code> in <code class="code">tbl</code>, restoring the previous binding if it exists. It does nothing if <code class="code">x</code> is not bound in <code class="code">tbl</code>.<br> </div> <pre><span id="VALreplace"><span class="keyword">val</span> replace</span> : <code class="type">('a, 'b) <a href="Hashtbl.html#TYPEt">t</a> -> 'a -> 'b -> unit</code></pre><div class="info"> <code class="code"><span class="constructor">Hashtbl</span>.replace tbl x y</code> replaces the current binding of <code class="code">x</code> in <code class="code">tbl</code> by a binding of <code class="code">x</code> to <code class="code">y</code>. If <code class="code">x</code> is unbound in <code class="code">tbl</code>, a binding of <code class="code">x</code> to <code class="code">y</code> is added to <code class="code">tbl</code>. This is functionally equivalent to <a href="Hashtbl.html#VALremove"><code class="code"><span class="constructor">Hashtbl</span>.remove</code></a><code class="code"> tbl x</code> followed by <a href="Hashtbl.html#VALadd"><code class="code"><span class="constructor">Hashtbl</span>.add</code></a><code class="code"> tbl x y</code>.<br> </div> <pre><span id="VALiter"><span class="keyword">val</span> iter</span> : <code class="type">('a -> 'b -> unit) -> ('a, 'b) <a href="Hashtbl.html#TYPEt">t</a> -> unit</code></pre><div class="info"> <code class="code"><span class="constructor">Hashtbl</span>.iter f tbl</code> applies <code class="code">f</code> to all bindings in table <code class="code">tbl</code>. <code class="code">f</code> receives the key as first argument, and the associated value as second argument. Each binding is presented exactly once to <code class="code">f</code>. The order in which the bindings are passed to <code class="code">f</code> is unspecified. However, if the table contains several bindings for the same key, they are passed to <code class="code">f</code> in reverse order of introduction, that is, the most recent binding is passed first.<br> </div> <pre><span id="VALfold"><span class="keyword">val</span> fold</span> : <code class="type">('a -> 'b -> 'c -> 'c) -> ('a, 'b) <a href="Hashtbl.html#TYPEt">t</a> -> 'c -> 'c</code></pre><div class="info"> <code class="code"><span class="constructor">Hashtbl</span>.fold f tbl init</code> computes <code class="code">(f kN dN ... (f k1 d1 init)...)</code>, where <code class="code">k1 ... kN</code> are the keys of all bindings in <code class="code">tbl</code>, and <code class="code">d1 ... dN</code> are the associated values. Each binding is presented exactly once to <code class="code">f</code>. The order in which the bindings are passed to <code class="code">f</code> is unspecified. However, if the table contains several bindings for the same key, they are passed to <code class="code">f</code> in reverse order of introduction, that is, the most recent binding is passed first.<br> </div> <pre><span id="VALlength"><span class="keyword">val</span> length</span> : <code class="type">('a, 'b) <a href="Hashtbl.html#TYPEt">t</a> -> int</code></pre><div class="info"> <code class="code"><span class="constructor">Hashtbl</span>.length tbl</code> returns the number of bindings in <code class="code">tbl</code>. Multiple bindings are counted multiply, so <code class="code"><span class="constructor">Hashtbl</span>.length</code> gives the number of times <code class="code"><span class="constructor">Hashtbl</span>.iter</code> calls its first argument.<br> </div> <br> <span id="6_Functorialinterface"><h6>Functorial interface</h6></span><br> <pre><span class="keyword">module type</span> <a href="Hashtbl.HashedType.html">HashedType</a> = <code class="code"><span class="keyword">sig</span></code> <a href="Hashtbl.HashedType.html">..</a> <code class="code"><span class="keyword">end</span></code></pre><div class="info"> The input signature of the functor <a href="Hashtbl.Make.html"><code class="code"><span class="constructor">Hashtbl</span>.<span class="constructor">Make</span></code></a>. </div> <pre><span class="keyword">module type</span> <a href="Hashtbl.S.html">S</a> = <code class="code"><span class="keyword">sig</span></code> <a href="Hashtbl.S.html">..</a> <code class="code"><span class="keyword">end</span></code></pre><div class="info"> The output signature of the functor <a href="Hashtbl.Make.html"><code class="code"><span class="constructor">Hashtbl</span>.<span class="constructor">Make</span></code></a>. </div> <pre><span class="keyword">module</span> <a href="Hashtbl.Make.html">Make</a>: <div class="sig_block"><code class="code"><span class="keyword">functor</span> (</code><code class="code"><span class="constructor">H</span></code><code class="code"> : </code><code class="type"><a href="Hashtbl.HashedType.html">HashedType</a></code><code class="code">) <span class="keywordsign">-></span> </code><code class="type"><a href="Hashtbl.S.html">S</a></code><code class="type"> with type key = H.t</code></div></pre><div class="info"> Functor building an implementation of the hashtable structure. </div> <br> <span id="6_Thepolymorphichashprimitive"><h6>The polymorphic hash primitive</h6></span><br> <pre><span id="VALhash"><span class="keyword">val</span> hash</span> : <code class="type">'a -> int</code></pre><div class="info"> <code class="code"><span class="constructor">Hashtbl</span>.hash x</code> associates a positive integer to any value of any type. It is guaranteed that if <code class="code">x = y</code> or <code class="code"><span class="constructor">Pervasives</span>.compare x y = 0</code>, then <code class="code">hash x = hash y</code>. Moreover, <code class="code">hash</code> always terminates, even on cyclic structures.<br> </div> <pre><span id="VALhash_param"><span class="keyword">val</span> hash_param</span> : <code class="type">int -> int -> 'a -> int</code></pre><div class="info"> <code class="code"><span class="constructor">Hashtbl</span>.hash_param n m x</code> computes a hash value for <code class="code">x</code>, with the same properties as for <code class="code">hash</code>. The two extra parameters <code class="code">n</code> and <code class="code">m</code> give more precise control over hashing. Hashing performs a depth-first, right-to-left traversal of the structure <code class="code">x</code>, stopping after <code class="code">n</code> meaningful nodes were encountered, or <code class="code">m</code> nodes, meaningful or not, were encountered. Meaningful nodes are: integers; floating-point numbers; strings; characters; booleans; and constant constructors. Larger values of <code class="code">m</code> and <code class="code">n</code> means that more nodes are taken into account to compute the final hash value, and therefore collisions are less likely to happen. However, hashing takes longer. The parameters <code class="code">m</code> and <code class="code">n</code> govern the tradeoff between accuracy and speed.<br> </div> </body></html>