A C++ generic Least Recently Used Cache
In general, I write software in Java for server side code or JavaScript for client (browser) user interface code. Over my career I have also written large software systems in C++. This includes compilers for the hardware design languages Verilog and VHDL, sensor monitoring and control software and physics simulation code.
I had a consulting opportunity for software development work in C++, so I needed to refresh my C++ knowledge. To help in this endeavor, I bought a copy of Bjarne Stroustrup's book "A Tour of C++". This book was the perfect reference for brushing up on my C++.
After reading through Stroustrup's book, I needed to write some code. I decided to implement a generic version of an LRU cache as a C++ template.
LRU caches have a number of applications. They can serve as a front end for a database, where the cache key is a database query, and the value is the query result. If the query is seen again while the {key, value} pair are stored in the cache, the cached value can be returned without referencing the database (this assumes that writes to the database also update the cache).
This implementation of the LRU cache uses the C++ standard template library (STL) unordered map. This map support O(1) access.