Scoping: Local vs Var - coldfusion

Question

I'm new to CF so this may be a basic question. But I've heard I should use local for objects inside functions due to how scoping works in CF. But what about 'var'? Is var the same as using local?
e.g.
function MyFunction()
{
local.obj = {};
}
Is this the same as:
function MyFunction()
{
var obj = {};
}
If they aren't the same, what is the difference between them? And when should I be using either of them?

Answer 1

They are very similar, but not exactly the same. Both only exist inside of a function but they work slightly differently.
The var version works it way through all the default variable scopes. See http://help.adobe.com/en_US/ColdFusion/9.0/Developing/WSc3ff6d0ea77859461172e0811cbec09af4-7fdf.html
Local will match only a variable in a local scope. Consider the following
<cffunction name="himom">
<cfoutput>
<p><b>try 0:</b> #request_method#</p>
<!--- you might think that the variable does not exist,
but it does because it came from cgi scope --->
</cfoutput>
<cfquery name="myData" datasource="Scorecard3">
SELECT 'This is via query' AS request_method
</cfquery>
<!--- Data is now being loaded into a query --->
<cfoutput query="myData">
<p><b>try 1:</b> #request_method#</p>
</cfoutput>
<!--- This one now came from the query --->
<cfset var request_method = "This is Var">
<!--- We now declare via var --->
<cfoutput query="myData">
<p><b>try 2:</b> #request_method#</p>
</cfoutput>
<!--- the query version disappears and now
the var version takes precedence --->
<cfset local.request_method = "This is local">
<!--- now we declare via local --->
<cfoutput query="myData">
<p><b>try 3:</b> #request_method#</p>
</cfoutput>
<!--- The local method takes precedence --->
<cfoutput>
<p><b>try 4:</b> #request_method#</p>
<!--- in fact it even takes precedence over the var --->
<p><b>try 5:</b> #local.request_method#</p>
<!--- there is no question where this comes from --->
</cfoutput>
</cffunction>
<cfset himom()>
Results of the above
try 0: GET
try 1: This is via query
try 2: This is Var
try 3: This is local
try 4: This is local
try 5: This is local
In summary
When developing, you could use either to make sure that variables only exist inside of a function, but always prefixing your variables with local goes a long way in making sure that your code is clearly understood

Answer 2

In ColdFusion 9+, using the local scope and the var directive in a ColdFusion CFC provide the same result.
Ben Forta explains it here:
http://forta.com/blog/index.cfm/2009/6/21/The-New-ColdFusion-LOCAL-Scope
I would recommend using the local. notation as it is more explicit.