Arrays vs. Slices: Which Offers Faster Element Access?

Array vs Slice: Accessing Speed

It is often assumed that arrays are faster than slices in accessing elements. However, benchmarking tests reveal a surprising result: local slices outperform local arrays.

The test benchmarked four functions: accessing global and local slices and arrays. Analyzing the results, global slices were indeed slightly slower than global arrays, aligning with expectations. However, local slices significantly outperformed local arrays.

Reason

Examining the amd64 assembly for both local array and slice benchmark functions, a notable difference emerges. The array version repeatedly loads the address of the array into memory during array-access operations, while the slice version performs computations exclusively on registers after loading from memory once.

Conclusion

This indicates that the extra step involved in accessing elements of a slice (by dereferencing the underlying array) is not a significant bottleneck for local variables. In this scenario, slices offer faster access due to more efficient use of registers. It's worth noting that this result may not hold true for large arrays or slices or when passed as function arguments.

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