Question

Which of these is more efficient in ColdFusion?

isDefined('url.myvar')

or

structKeyExists(url, 'myvar')

Answer 1

These days (CF8+) the difference in speed is not that great. However, structKeyExists is indeed a little faster. Here’s why.

When you use isDefined, the string you pass in is searched for as a key name in several scopes. As of CF9, the list of scopes, in the order checked is: (source)

1. Local (function local, UDFs and CFCs only)
2. Arguments
3. Thread local (inside threads only)
4. Query (not a true scope, applies for variables within query loops)
5. Thread
6. Variables
7. CGI
8. CFFile
9. URL
10. Form
11. Cookie
12. Client

Even if you use the scope name with isDefined (like: if isDefined('variables.foo')) the list will still be checked in order; and if the variable local.variables.foo is defined, it will be found BEFORE variables.foo.

On the other hand, structKeyExists only searches the structure you pass it for the existence of the key name; so there are far fewer places it will have to look.

By using more explicit code (structKeyExists), not only are you gaining some performance, but your code is more readable and maintainable, in my opinion.