Wednesday, January 17, 2007

Optimizations with literals

Look at these two pieces of code carefully. Is there any difference between these two apart from the fact that the second one is shorter?

<cfset x = "sun,mercury,venus,earth,mars,jupiter,saturn,uranus,pluto,neptune">
<cfset y = ListSort(x,"text")>


<cfset y = ListSort("sun,mercury,venus,earth,mars,jupiter,saturn,uranus,pluto,neptune","text")>

If you think there is not much, read on.

There is a huge difference between these two piece of code - in terms of performance. The second one will have much better performance as compared to the first one. How?? Because the ListSort() method in the second case will not even be executed in the page request. Still scratching your head?

It is because of the intelligence that is built into CFML compiler (really superb code written by Edwin Smith). During compilation, it analyzes all the code and wherever there is a literal or functions executing literals, it tries to optimize it. In the second piece here, it sees that ListSort method is being called on a literal and it can be done statically. So compiler will execute this call during compilation itself and set the sorted value on 'y'. During the page execution, only thing that will get executed will be an assignment. Smart.. isn't it? Even java compiler, which does quite a many compile time optimization for java source files, does not have this intelligence of executing calls at compile time :)

It is not only about 'ListSort'. This is true for most of those CF functions which can work on a literal and can return a literal.


Josh Giese said...

WOW, that a really awesome trick. I will have to keep that in mind when I am optimizing my coldfusion. Thanks for posting this.

Ben Nadel said...

That is a cool little trick.