When to use duplicate()

Hi Ian,

Now now, not not.

Got it. I had an inkling it had to do with the devil in the machine.

BKBK wrote:
> Ian,
>
> Did you really mean to say, "Duplicating (cloneing) a variable copies the value to a new memory location so that it is not a separate entity.
> "?
>
>

No, that should have said "..so that it is now a separate ...".
But once it was sent and I noticed my slip of a finger, there isn't a
way for me to edit the message from the newsgroup.

And I just despise the web interface, so I'm not going to go there just
for one letter.

Ian,

Did you really mean to say, "Duplicating (cloneing) a variable copies the value to a new memory location so that it is not a separate entity.
"?

A little addition to Adam's code to make it more implicit on what is
happening.

{code}
<cffunction name="showIt">
<cfargument name="aVar">
<cfargument name="aLable">

<cfdump var="#arguments.aVar#" label="#arguments.aLable#">
</cffunction>

<cfscript>
st1 = structNew();
st1.firstName = "Adam";
st1.lastName = "Cameron";
showIt(st1,"ST1");
writeOutput("<hr/>");

st2 = st1;
showIt(st1,"ST1");
showIt(st2,"ST2");
writeOutput("<hr/>");

st2.firstName = "Someone";
st2.lastName = "Else";
showIt(st1,"ST1");
showIt(st2,"ST2");
writeOutput("<hr/>");

st3 = duplicate(st1);
showIt(st1,"ST1");
showIt(st2,"ST2");
showIt(st3,"ST3");
writeOutput("<hr/>");

st3.firstName = "Third";
st3.lastName = "Person";
showIt(st1,"ST1");
showIt(st2,"ST2");
showIt(st3,"ST3");
</cfscript>

> Yes, I did read the docs.

OK, was just checking if you'd tried to help yourself. Heaps of people
here do not.

This code demonstrates copy-by-value (duplicate) vs copy-by-reference
(assignment operator).

{code}
<cfscript>
st1 = structNew();
st1.firstName = "Adam";
st1.lastName = "Cameron";

st2 = st1;
st2.firstName = "Someone";
st2.lastName = "Else";

st3 = duplicate(st1);
st3.firstName = "Third";
st3.lastName = "Person";
</cfscript>

<cfdump var="#variables#">
{code}

st1 and st2 are both references to the same object. st3 is a different
object than st1, created with the same initial values.

Make sense?

--
Adam

> The former is done to save memory and ColdFusion does this with complex
> variable types such as arrays, structures and objects. It does not do
> this with simple variables such as numbers and strings.

Arrays, as far as I know, are copied by value. Not that intuitive given
how CF seems to copy "all" other complesx types by reference.

--
Adam

SpiderFromMars wrote:
> Yes, I did read the docs. It talks about returning a clone. But, my question
> is: What is the difference between returning a clone and between referencing
> the variable directly. What is the benefit of it?
>


Two variables that are a reference are pointing to the same value in the
same memory location. Thus if you change the value with variableA, then
the value of variableB changes.

Duplicating (cloneing) a variable copies the value to a new memory
location so that it is not a separate entity.

The former is done to save memory and ColdFusion does this with complex
variable types such as arrays, structures and objects. It does not do
this with simple variables such as numbers and strings.

Yes, I did read the docs. It talks about returning a clone. But, my question is: What is the difference between returning a clone and between referencing the variable directly. What is the benefit of it?

> What's the difference between:
> <cfset x = y>
> and
> <cfset x = duplicate(y)>

As a first port of call: did you read the docs?

http://livedocs.adobe.com/coldfusion/8/functions_c-d_47.html

--
Adam