Everything old is new again: memory optimization

Summary

At this point in history, AI sociopaths have purchased all the world's RAM in order to run their copyright infringement factories at full blast. Thus the amount of memory in consumer computers and phones seems to be going down. After decades of not having to care about memory usage, reducing it has very much become a thing.Relevant questions to this state of things include a) is it really worth it and b) what sort of improvements are even possible. The answers to these depend on the task and data set at hand. Let's examine one such case. It might be a bit contrived, unrepresentative and unfair, but on the other hand it's the one I already had available.Suppose you have to write script that opens a text file, parses it as UTF-8, splits it into words according to white space, counts the number of time each word appears and prints the words and counts in decreasing order (most common first).The Python baselineThis sounds like a job for Python. Indeed, an implementation takes fewer than 30 lines of code. Its memory consumption on a small text file looks like this.Peak memory consumption is 1.3 MB. At this point you might want to stop reading and make a guess on how much memory a native code version of the same functionality would use.The native versionA fully native C++ version using Pystd requires 60 lines of code to implement the same thing. If you ignore the boilerplate, the core functionality fits in 20 lines. The steps needed are straightforward:Mmap the input file to memory.Validate that it is utf-8Convert raw data into a utf-8 viewSplit the view into words lazilyCompute the result into a hash table whose keys are string views, not stringsThe main advantage of this is that there are no string objects. The only dynamic memory allocations are for the hash table and the final vector used for sorting and printing. All text operations use string views , which are basically just a pointer + size.In code this looks like the following:Its memory usage looks like this.Peak...