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<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="moz-cite-prefix">On 06/29/2018 03:35 AM, Dmytro
Lytovchenko wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAOUb9CEMVFZRyMtnbaZ7Vp3p0hnT7W8Pa1PTvEudEqk=XV=aKg@mail.gmail.com">
<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"
moz-do-not-send="true">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"
moz-do-not-send="true">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"
moz-do-not-send="true">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_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"
moz-do-not-send="true">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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<br>
<pre class="moz-signature" cols="72">--
BR,
Dmitry
</pre>
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