> And just use the built-in ones don't invent your own unless there is a very good reason for it.
Uhm, hash tables are one of these things where plenty can be gained by tailoring the structure to the application. It's not a one-size-fits-all, and it's not nearly as easy as it would seem to make a good general-purpose HT.
Built-in implementations usually are kind of slow, waste memory, have broken iterators [1], even in modern languages. If either of those things are important - it's better to do some research and maybe even invent your own.
[1] when you can't both iterate and insert items consistently in the same loop
It's often true due to a few factors. One is that they are safe, whereas a specific use case may not need the same level of safety. They generally optimize for the general case as well, but in your own code you can optimize for the very specific use case you have. One I ran into many years ago was implementing my own singly linked list by adding the next pointer to another piece of data. In this one specific case it was worth removing another layer of indirection. I was still young though, so there were probably even better ways of handling it.
I have only encountered these scenarios a small handful of times, but I'm not a very low level developer.
I can see if this was published in late 90's but today, I don't know.
And just use the built-in ones don't invent your own unless there is a very good reason for it.