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Differences in Creating Copy of a Structure Using CFSet, Duplicate, and Structcopy in ColdFusion

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Most ColdFusion developers get confused between the CFSet, Duplicate, and Structcopy methods of copying a Structure, especially which one to use when. This Article will explain the differences in the approaches with examples; therefore, after reading, you should get a clear understanding of what each does and which one is best in a given scenario.

Using CFSet

Creating a copy of a Structure using CFSet will result in a new variable having a reference to the original Structure; therefore, changes will affect the original Structure.

Example:
<cfset structtest = structnew()>
<cfset structtest.txt = "Testing">
<cfset structtest.nestedstruc = structnew()>
<cfset structtest.nestedstruc[1] = "sri">
<cfset structtest.nestedstruc[2] = "Kanth">
<cfset Variables.st1 = structtest>

<cfdump var="#structtest#" label="original structtest Structure">

<cfdump var="#st1#" label="st1 struct - using Cfset">

<cfset st1.txt = "Testing1">
<cfset st1.nestedstruc[2] = "Kanth M">
<h3> After assigning Values </h3>
<cfdump var="#structtest#" label="original Session Structure">

<cfdump var="#st1#" label="st1 struct - using Cfset">

Open in new window

Using CFSet
In the above code, we have a Structure structtest with a simple variable txt and nested Structure nestedstruc.
Since st1 references structtest, we can see that values updated for txt and nestedstruc of st1 are also reflected in the original Structure structtest.

Using Duplicate

Creating a copy of a Structure using Duplicate will result in a new variable containing no reference to the original Structure but rather a snapshot of its current contents.

Example:
<cfset structtest = structnew()>
<cfset structtest.txt = "Testing">
<cfset structtest.nestedstruc = structnew()>
<cfset structtest.nestedstruc[1] = "sri">
<cfset structtest.nestedstruc[2] = "Kanth">
<cfset Variables.st1 = duplicate(structtest)>

<cfdump var="#structtest#" label="original structtest Structure">

<cfdump var="#st1#" label="st1 struct - using Duplicate">

<cfset st1.txt = "Testing1">
<cfset st1.nestedstruc[2] = "Kanth M">
<h3> After assigning Values </h3>
<cfdump var="#structtest#" label="original Session Structure">

<cfdump var="#st1#" label="st1 struct - using Duplicate">

Open in new window

Using Duplicate
In the above sample, we can see that the values updated for txt and nestedstruc of st1 are not reflected in the original Structure structtest.

Using Strcutcopy

Strcutcopy is where most people get confused.
We can say Structcopy is between CFSet and Duplicate.
When we use Structcopy, a new structure will be created; however, references to nested structures, objects, and query variables will be maintained from the original Structure.

Example:
<cfset structtest = structnew()>
<cfset structtest.txt = "Testing">
<cfset structtest.nestedstruc = structnew()>
<cfset structtest.nestedstruc[1] = "sri">
<cfset structtest.nestedstruc[2] = "Kanth">
<cfset Variables.st1 = structcopy(structtest)>

<cfdump var="#structtest#" label="original structtest Structure">

<cfdump var="#st1#" label="st1 struct - using structcopy">

<cfset st1.txt = "Testing1">
<cfset st1.nestedstruc[2] = "Kanth M">
<h3> After assigning Values </h3>
<cfdump var="#structtest#" label="original Session Structure">

<cfdump var="#st1#" label="st1 struct - using structcopy">

Open in new window

Using Structcopy
In the above example, we can see that the change for txt is not reflected in the original Structure, but the "2" key change of the nested nestedstruc Structure is reflected in the structtest Structure .

Conclusion

Try to use the best one while copying a Structure which will be more effective for your scenario:
Cfset – Create a reference to the original Structure.
Duplicate – Create a new Structure with no reference to the original Structure.
Structcopy – Create a new Structure with references to the complex variables contained in the original Structure like nested structures, objects, and query variables.
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