Sometimes I want to provide an optional lambda to ...

# general-advice

[Landry Norris]

Sometimes I want to provide an optional lambda to a method. From a performance standpoint, is it better to make the lambda nullable and check if(lambda != null) lambda() or will I get better performance setting lambda = {} by default and always calling it? I get that both should be fast, but I’d like to minimize overhead in a hot spot. This code is for both K/JVM and K/Native.

[Klitos Kyriacou]

You should measure the performance in your own application, on the target machine and with the compiler/runtime version that will be used in production, since different environments can give different results. My hunch is that checking a null lambda would be prone to branch misprediction, which is expensive, so I would favour the empty lambda idea. However, someone has already tested these two scenarios, albeit in an old version of Java, back in 2015, and found varying results: https://stackoverflow.com/questions/22890326/is-defaulting-to-an-empty-lambda-better-or-worse-than-checking-for-a-potentially. If you search, you'll find various other reports on the subject too.

[Landry Norris]

Thanks. I noticed when I looked through some source code in Compose that they had some global variables set to empty lambdas, with a note about how it’s faster than passing in an empty lambda literal. I can see how the C2 compiler for JVM would make nullable faster (that was one of the C2's optimizations if I remember correctly). I wonder how native will be affected. I’ll have to write some experimental code to test at some point.

[Sam Stone]

Keep us posted!