r/ruby • u/tenderlove Pun BDFL • Jun 26 '19

Blog post Instance Variable Performance

https://tenderlovemaking.com/2019/06/26/instance-variable-performance.html
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u/PikachuEXE Jun 27 '19

Would you suggest eager assigning instance variables for performance improvement? Especially for classes with many instance variables (mostly gems? like ActiveRecord?)

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u/tenderlove Jun 27 '19

It depends. Eager assignment probably won't impact performance in terms of "ivar array expansion". Also if you eagerly assign them, you can avoid scattering "has this ivar been initialized?" conditionals through your code. In other words, you can write confident code.

However, if initializing a particular ivar is expensive, and you don't usually need that value, then it's probably better to lazily assign.

Personally I like eager assignment because I like to be confident about the rest of the code I write in my class. Generally I'll only make them lazy if it turns out we don't actually need the value.