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When using Array.GetLength(dimension) in C#, does the size of the array actually get calculated each time it is called, or is the size cached/stored and that value just gets accessed?
What I really want to know is if setting a local variable to the length of the dimension of an array would add any efficiency if used inside a big loop or if I can just call array.GetLength() over and over w/o any speed penalty.
It is most certainly a bad idea to start caching/optimizing by yourself here.
When dealing with arrays, you have to follow a standard path that the (JIT) optimizer can recognize. If you do, not only will the Length property be cached but more important the index bounds-check can be done just once before the loop.
When the optimizer loses your trail you will pay the penalty of a per-access bounds-check.
This is why jagged arrays (
int[][]) are faster than multi-dim (int[,]). The optimization forint[,]is simply missing. Up to Fx2 anyway, I didn’t check the status of this in Fx4 yet.If you want to research this further, the caching you propose is usually called ‘hoisting‘ the Length property.