Dynamic is FAST!


Dynamic is FAST!

The dynamic keyword introduced in C# 4.0 can be really handy. But what’s the cost?

I was a bit nervous after reading the incredible Mr. Lippert. So I tested it.

I created two console projects based on my Replace Conditional with Polymorphism example. There are 7 subtypes, the overloads call Trace.WriteLine (to avoid I/O overhead), and the caller never sends an unknown type (to avoid exception overhead and match the real world). I compiled in debug mode and verified that the calls did not get optimized out. The programs use a Stopwatch around a loop, which calls the MakeAnimalNoise method once for each subtype.

The results surprised me.

Time (hh:mm:ss.fractions) for 100000 trials without dynamic: 

Time (hh:mm:ss.fractions) for 100000 trials with dynamic: 

Timing the runs with a physical stopwatch, I didn’t see any significant difference in startup times, either. (My measurements here were far from exact.)

Binary file sizes are comparable. I did not have the tools to measure memory footprints.

Based on these tests I’m comfortable with using dynamic code from a performance standpoint. Thank you Microsoft!

Update - March 6, 2011

I suspect this example takes full advantage of internal DLR caching; your mileage may vary.

See also Eric Lippert on memory impact and garbage collection.

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