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<link title="Weak" rel="Chapter" href="Weak.html"><link title="Low-level functions" rel="Section" href="#6_Lowlevelfunctions">
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<title>Weak</title>
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<center><h1>Module <a href="type_Weak.html">Weak</a></h1></center>
<br>
<pre><span class="keyword">module</span> Weak: <code class="type">sig end</code></pre><div class="info">
Arrays of weak pointers and hash tables of weak pointers.<br>
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<a name="6_Lowlevelfunctions"></a>
<table cellpadding=5 cellspacing=5 width="100%">
<tr class="title6"><td><div align=center>
<span class="title6">Low-level functions</span>
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<br><br>
<br><code><span class="keyword">type</span> <a name="TYPEt"></a><code class="type">'a</code> t </code>
<div class="info">
The type of arrays of weak pointers (weak arrays). A weak
pointer is a value that the garbage collector may erase at
any time.
A weak pointer is said to be full if it points to a value,
empty if the value was erased by the GC.<br>
</div>
<br>
<pre><span class="keyword">val</span> <a name="VALcreate"></a>create : <code class="type">int -> 'a <a href="Weak.html#TYPEt">t</a></code></pre><div class="info">
<code class="code"><span class="constructor">Weak</span>.create n</code> returns a new weak array of length <code class="code">n</code>.
All the pointers are initially empty. Raise <code class="code"><span class="constructor">Invalid_argument</span></code>
if <code class="code">n</code> is negative or greater than <a href="Sys.html#VALmax_array_length"><code class="code"><span class="constructor">Sys</span>.max_array_length</code></a><code class="code">-1</code>.<br>
</div>
<pre><span class="keyword">val</span> <a name="VALlength"></a>length : <code class="type">'a <a href="Weak.html#TYPEt">t</a> -> int</code></pre><div class="info">
<code class="code"><span class="constructor">Weak</span>.length ar</code> returns the length (number of elements) of
<code class="code">ar</code>.<br>
</div>
<pre><span class="keyword">val</span> <a name="VALset"></a>set : <code class="type">'a <a href="Weak.html#TYPEt">t</a> -> int -> 'a option -> unit</code></pre><div class="info">
<code class="code"><span class="constructor">Weak</span>.set ar n (<span class="constructor">Some</span> el)</code> sets the <code class="code">n</code>th cell of <code class="code">ar</code> to be a
(full) pointer to <code class="code">el</code>; <code class="code"><span class="constructor">Weak</span>.set ar n <span class="constructor">None</span></code> sets the <code class="code">n</code>th
cell of <code class="code">ar</code> to empty.
Raise <code class="code"><span class="constructor">Invalid_argument</span> <span class="string">"Weak.set"</span></code> if <code class="code">n</code> is not in the range
0 to <a href="Weak.html#VALlength"><code class="code"><span class="constructor">Weak</span>.length</code></a><code class="code"> a - 1</code>.<br>
</div>
<pre><span class="keyword">val</span> <a name="VALget"></a>get : <code class="type">'a <a href="Weak.html#TYPEt">t</a> -> int -> 'a option</code></pre><div class="info">
<code class="code"><span class="constructor">Weak</span>.get ar n</code> returns None if the <code class="code">n</code>th cell of <code class="code">ar</code> is
empty, <code class="code"><span class="constructor">Some</span> x</code> (where <code class="code">x</code> is the value) if it is full.
Raise <code class="code"><span class="constructor">Invalid_argument</span> <span class="string">"Weak.get"</span></code> if <code class="code">n</code> is not in the range
0 to <a href="Weak.html#VALlength"><code class="code"><span class="constructor">Weak</span>.length</code></a><code class="code"> a - 1</code>.<br>
</div>
<pre><span class="keyword">val</span> <a name="VALget_copy"></a>get_copy : <code class="type">'a <a href="Weak.html#TYPEt">t</a> -> int -> 'a option</code></pre><div class="info">
<code class="code"><span class="constructor">Weak</span>.get_copy ar n</code> returns None if the <code class="code">n</code>th cell of <code class="code">ar</code> is
empty, <code class="code"><span class="constructor">Some</span> x</code> (where <code class="code">x</code> is a (shallow) copy of the value) if
it is full.
In addition to pitfalls with mutable values, the interesting
difference with <code class="code">get</code> is that <code class="code">get_copy</code> does not prevent
the incremental GC from erasing the value in its current cycle
(<code class="code">get</code> may delay the erasure to the next GC cycle).
Raise <code class="code"><span class="constructor">Invalid_argument</span> <span class="string">"Weak.get"</span></code> if <code class="code">n</code> is not in the range
0 to <a href="Weak.html#VALlength"><code class="code"><span class="constructor">Weak</span>.length</code></a><code class="code"> a - 1</code>.<br>
</div>
<pre><span class="keyword">val</span> <a name="VALcheck"></a>check : <code class="type">'a <a href="Weak.html#TYPEt">t</a> -> int -> bool</code></pre><div class="info">
<code class="code"><span class="constructor">Weak</span>.check ar n</code> returns <code class="code"><span class="keyword">true</span></code> if the <code class="code">n</code>th cell of <code class="code">ar</code> is
full, <code class="code"><span class="keyword">false</span></code> if it is empty. Note that even if <code class="code"><span class="constructor">Weak</span>.check ar n</code>
returns <code class="code"><span class="keyword">true</span></code>, a subsequent <a href="Weak.html#VALget"><code class="code"><span class="constructor">Weak</span>.get</code></a><code class="code"> ar n</code> can return <code class="code"><span class="constructor">None</span></code>.<br>
</div>
<pre><span class="keyword">val</span> <a name="VALfill"></a>fill : <code class="type">'a <a href="Weak.html#TYPEt">t</a> -> int -> int -> 'a option -> unit</code></pre><div class="info">
<code class="code"><span class="constructor">Weak</span>.fill ar ofs len el</code> sets to <code class="code">el</code> all pointers of <code class="code">ar</code> from
<code class="code">ofs</code> to <code class="code">ofs + len - 1</code>. Raise <code class="code"><span class="constructor">Invalid_argument</span> <span class="string">"Weak.fill"</span></code>
if <code class="code">ofs</code> and <code class="code">len</code> do not designate a valid subarray of <code class="code">a</code>.<br>
</div>
<pre><span class="keyword">val</span> <a name="VALblit"></a>blit : <code class="type">'a <a href="Weak.html#TYPEt">t</a> -> int -> 'a <a href="Weak.html#TYPEt">t</a> -> int -> int -> unit</code></pre><div class="info">
<code class="code"><span class="constructor">Weak</span>.blit ar1 off1 ar2 off2 len</code> copies <code class="code">len</code> weak pointers
from <code class="code">ar1</code> (starting at <code class="code">off1</code>) to <code class="code">ar2</code> (starting at <code class="code">off2</code>).
It works correctly even if <code class="code">ar1</code> and <code class="code">ar2</code> are the same.
Raise <code class="code"><span class="constructor">Invalid_argument</span> <span class="string">"Weak.blit"</span></code> if <code class="code">off1</code> and <code class="code">len</code> do
not designate a valid subarray of <code class="code">ar1</code>, or if <code class="code">off2</code> and <code class="code">len</code>
do not designate a valid subarray of <code class="code">ar2</code>.<br>
</div>
<br>
<br>
<a name="6_Weakhashtables"></a>
<table cellpadding=5 cellspacing=5 width="100%">
<tr class="title6"><td><div align=center>
<span class="title6">Weak hash tables</span>
</div>
</td>
</tr>
</table>
<br><br>
<br>
A weak hash table is a hashed set of values. Each value may
magically disappear from the set when it is not used by the
rest of the program any more. This is normally used to share
data structures without inducing memory leaks.
Weak hash tables are defined on values from a <a href="Hashtbl.HashedType.html"><code class="code"><span class="constructor">Hashtbl</span>.<span class="constructor">HashedType</span></code></a>
module; the <code class="code">equal</code> relation and <code class="code">hash</code> function are taken from that
module. We will say that <code class="code">v</code> is an instance of <code class="code">x</code> if <code class="code">equal x v</code>
is <code class="code"><span class="keyword">true</span></code>.
<p>
The <code class="code">equal</code> relation must be able to work on a shallow copy of
the values and give the same result as with the value itself.<br><br>
<pre><span class="keyword">module type</span> <a href="Weak.S.html">S</a> = <code class="type">sig end</code></pre><div class="info">
The output signature of the functor <a href="Weak.Make.html"><code class="code"><span class="constructor">Weak</span>.<span class="constructor">Make</span></code></a>.
</div>
<pre><span class="keyword">module</span> <a href="Weak.Make.html">Make</a>: <code class="type">functor (H : <a href="Hashtbl.HashedType.html">Hashtbl.HashedType</a>) -> sig end</code></pre><div class="info">
Functor building an implementation of the weak hash table structure.
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