Introduction:
STL is a great library, and useful in many cases, but it definitively don't solve all the situations. Answering STL or !STL is like answering "Does STL meet your need or does it not?"
Pros of STL
- In most situations, STL has a container that fit for a given solution.
- It is well documented
- It is well known ( Programmers usually already know it, getting into a project is shorter)
- It is tested and stable.
- It is crossplatform
- It is included with every compiler (does not add a 3rd library dependency)
- STL is already implemented and ready
- STL is shiny, ...
Contras of STL
It does not mater that you need a simple Graph, Red-Black Tree, or a very complex database of elements with an AI managing concurrent access through a quantum computer. The fact is, STL do not, and will never solve everything.
Following aspects are only a few examples, but they basically are consequence of this fact: STL is a real library with limits.
Exceptions: STL relay on exceptions, so if for any reason you cannot accept exceptions (e.g. safety critical), you cannot use STL. Right! exceptions may be disabled, but that does not solve the design of the STL relaying on them and will eventually carry a crash.
Need of specific (not yet included) data structure: graph, tree, etc.
Special constraints of complexity: You could discover that STL general purpose container is not the most optimal for your bottleneck code.
Concurrency considerations: Either you need concurrency and STL do not provide what you need (e.g. reader-writer lock cannot(easily) be used because of the bi-directional [] operator). Either you could design a container taking benefit of multi-threading for a much faster access/searching/inserting/whatever.
STL need to fit your needs, but the revers is also true: You need to fulfill the needs of STL. Don't try to use std::vector in a embedded micro-controller with 1K of unmanaged RAM.
Compatibility with other libraries: It may be that for historical reasons, the libraries you use do not accept STL (e.g. QtWidgets make intensive use of it own QList). Converting containers in both directions might be not the best solution.
Implementing your own container
After reading that, you could think: "Well, I am sure I may do something better for my specific case than STL does." WAIT!
Implementing your container correctly become very quickly a huge task: it is not only about implementing something working, you might have to:
- Document it deeply, including limitations, algorithm complexity,etc.
- Expect bugs, and solving them
- Incoming additional needs: you know, this function missing, this conversion between types, etc.
- After a while, you could want to refactor, and change all the dependencies (too late?)
- ....
Code used that deep in the code like a container is definitively something that take time to implement, and should be though carefully.
Using 3rd party library
Not STL does not necessarily mean custom. There are plenty of good libraries in the net, some even with permissive open-source license.
Adding or not an additional 3rd party library is another topic, but it worth to be considered.
