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<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff size=2>In the
example you give they share memory.</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff size=2>Record
= #some_record()</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2>Creates a record - this is actually stored on the
heap.</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff size=2>The
local variable Record or the arguments to the functions are
just</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff size=2>tagged
pointers.</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2>Virtually all objects in Erlang are represented by tagged pointers
which fit into 32 bits</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff size=2>(on a
32 bit machine) - exceptions are things like small integers, and the
empty list.</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff size=2>If you
say</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=909595613-04072006> <FONT face=Arial
color=#0000ff size=2>X = {1,2,3}</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006> <FONT face=Arial
color=#0000ff size=2>foo(X).</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2>Then</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=909595613-04072006> <FONT face=Arial
color=#0000ff size=2>foo(X) -></FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2> Y = g(X),</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006> <FONT face=Arial
color=#0000ff size=2> ...</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff size=2>Thing
of X = {1,2,3} as doing the following:</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff size=2>First
malloc space for a {1,2,3} structure on the heap.</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff size=2>Then
create the {1,2,3} structure. Put a tagged pointer to</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff size=2>the
malloced area on the heap into X.</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff size=2>X is
(internally) a 32 bit tagged pointer. This pointer is passed into foo
and</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff size=2>so
on.</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff size=2>Heap
data structures are garbage collected when they can no longer
be</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2>referred to. So after the call to g(X) the space used by X can be
reclaimed,</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff size=2>if
there are no other references to X.</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2>/Joe</FONT></SPAN></DIV>
<DIV><SPAN class=909595613-04072006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=909595613-04072006> </SPAN></DIV>
<DIV><SPAN class=909595613-04072006> </SPAN><SPAN
class=909595613-04072006><FONT face=Arial color=#0000ff
size=2> </FONT></SPAN></DIV><BR>
<BLOCKQUOTE dir=ltr
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px solid; MARGIN-RIGHT: 0px">
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left>
<HR tabIndex=-1>
<FONT face=Tahoma size=2><B>From:</B> owner-erlang-questions@erlang.org
[mailto:owner-erlang-questions@erlang.org] <B>On Behalf Of </B>Yani
Dzhurov<BR><B>Sent:</B> den 4 juli 2006 15:43<BR><B>To:</B>
erlang-questions@erlang.org<BR><B>Subject:</B> are function parameters
copied?<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV class=Section1>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Hi,<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><o:p> </o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">I’ve wondered whether functions
share memory or for a function call new memory is allocated and parameters are
copied ?<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">This is what I
mean:<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">fun()-><o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">
Record = #some_record{},<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">
fun1(Record).<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><o:p> </o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">fun1(Record)-><o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">
fun2(Record).<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">fun2(Record)-><o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">
fun3(Record).<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">.fun3(Record)-><o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">
fun4(Record).<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">fun4(Record)-><o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">
Some operations with records….<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><o:p> </o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Is the VM going to copy Record
four times for each function call or all functions will share this object
Record…having in mind that it’s immutable this shouldn’t be a
problem?<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><o:p> </o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Thanks,<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><o:p> </o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Jani<o:p></o:p></SPAN></FONT></P></DIV></BLOCKQUOTE></BODY></HTML>