Performance deep dive

In this article, we'll examine the performance difference between approaches for reverse-string in Crystal.

The approaches page lists three approaches to this exercise:

1. Using the built-in reverse method
2. Using an array
3. Using String::Builder

Benchmarks

To benchmark the approaches, we wrote a small benchmark application using the built-in Benchmark module. These tests were run in WSL2, using Crystal 1.10.1. Your system results may vary.

ReverseString, short string
  0.000000   0.000001   0.000001 (  0.000001)
ReverseStringArray, short string
  0.000000   0.000004   0.000004 (  0.000004)
ReverseStringStringBuild, short string
  0.000000   0.000000   0.000000 (  0.000001)
ReverseString, long string
  0.000000   0.000011   0.000011 (  0.000011)
ReverseStringArray, long string
  0.000000   0.000088   0.000088 (  0.000088)
ReverseStringStringBuild, long string
  0.000000   0.000051   0.000051 (  0.000051)

Conclusion

As we can see, the built-in reverse method is the fastest approach for both short and long strings. The String::Builder approach is the second fastest, and the array approach is the slowest. This is likely due to the fact that the array approach requires converting the string to an array, and then converting the array back to a string.

Although what can also be noticed is that giving the size of the string to the String::Builder and the array approach is faster than not giving the size.