<div dir="ltr">Has there been some testing / measurements done on the memory saved by introducing a "tuple of 2" tag only for 2-tuples?<div>{ok, Bla} or {error, R} is such a common pattern and "most" machines being 64bits nowadays this should save many times 8 bytes, shouldn't it?</div><div>So we have a tag for lists (cons), a tag for n-sized tuples and tags for other data. How about a tag for a memory structure that's basically [a|b] but which would be understood as {a,b}.</div><div><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div><br></div><div>Cheers,</div><div>-- </div><div>Pierre Fenoll</div></div><div><br></div></div></div></div><br></div></div><br><div class="gmail_quote"><div dir="ltr">On Fri, 29 Jun 2018 at 10:16, Dmitry Klionsky <<a href="mailto:dm.klionsky@gmail.com">dm.klionsky@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<p>Some numbers <br>
</p>
<p>1> erts_debug:flat_size([a,b]).<br>
4<br>
2> erts_debug:flat_size({a,b}).<br>
3<br>
3> erts_debug:flat_size([a|b]).<br>
2<br>
<br>
</p>
<br>
<div class="m_-862425632789854890moz-cite-prefix">On 06/29/2018 03:35 AM, Dmytro
Lytovchenko wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div>A tuple of 2 elements will take 3 words of memory minimum</div>
<div><a href="http://beam-wisdoms.clau.se/en/latest/indepth-memory-layout.html#tuple-arityval-0" target="_blank">http://beam-wisdoms.clau.se/en/latest/indepth-memory-layout.html#tuple-arityval-0</a></div>
<div>tuple1 = [ headerWord, element1, element2 ]<br>
</div>
<div><br>
</div>
<div>A cons cell has no header word, so an improper list of 1
element and 2nd element as a tail, just 2 values stored side
to side<br>
</div>
<div>(same as normal list below except that only 1 cons cell is
used, 2 words)</div>
<div>cons1 = [ element1, element2 ]<br>
</div>
<div><br>
</div>
<div>
<div>A proper list of 2 elements will take 2 cons cells, i.e.
4 words of memory minimum</div>
<div>cons2 = [ element2, [] ]<br>
</div>
<div>cons1 = [ element1, cons2 ]<br>
</div>
<div><a href="http://beam-wisdoms.clau.se/en/latest/indepth-memory-layout.html#lists-cons" target="_blank">http://beam-wisdoms.clau.se/en/latest/indepth-memory-layout.html#lists-cons</a><br>
</div>
<div><br>
</div>
</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">2018-06-29 2:23 GMT+02:00 Dmitry
Belyaev <span dir="ltr"><<a href="mailto:be.dmitry@gmail.com" target="_blank">be.dmitry@gmail.com</a>></span>:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">
<div>It's a way to reduce memory footprint.</div>
<div><br>
</div>
<div>Tuple of size N is roughly represented in memory as
an array [TupleTag, N, TupleElement1, TupleElement2,
..., TupleElementN].</div>
<div>Compare it to Cons cell representation: [ConsTag,
HeadElement, TailElement] - it saves 1 word per
structure.<br>
</div>
<div class="gmail_extra"><br clear="all">
<div>
<div class="m_-862425632789854890m_7606740003781037632m_2917007213273080743gmail_signature" data-smartmail="gmail_signature">
<div dir="ltr">Kind regards,
<div>Dmitry Belyaev</div>
</div>
</div>
</div>
<br>
<div class="gmail_quote">On Fri, Jun 29, 2018 at 9:50
AM, Karlo Kuna <span dir="ltr"><<a href="mailto:kuna.prime@gmail.com" target="_blank">kuna.prime@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">dealing with digraph module i have
noticed use of improper lists as representations
of edges: <br>
['$e' | 123]
<div><br>
</div>
<div>is there a good reason to use improper lists
instead of tuple for this and in general </div>
<div>when is a good idea to use improper lists??
(i can't think of example for justified use)</div>
</div>
<br>
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<pre class="m_-862425632789854890moz-signature" cols="72">--
BR,
Dmitry
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