I got into a discussion about code reuse with my co-worker, Jarek. I remember reading books on object oriented programming from a few decades ago in which OOP promised to increase code reuse. A lot of people doubted that serious code reuse would ever happen. OOP suggested that code reuse would be possible by reusing and subclassing existing classes. I even remember hearing C++ programmers talk about purchasing libraries of useful classes.
To some degree, this did actually happen. For instance, QT is a wonderful library for C++, and it certainly makes coding in C++ a lot easier. It was even proprietary up until a few years ago. Library reuse also happened via language-specific package sites such as CPAN (for Perl), PyPI (for Python), and a range of sites for Ruby. Furthermore, most languages come with a lot more stuff built in these days. For instance, compare Python's standard library ("batteries included") with that of C.
However, compared to decades ago, there is less of an emphasis on class-level reuse these days. For instance, rather than trying to code classes that will be flexible enough to solve tomorrow's problems, agile programmers suggests you write your code in such a way that you will be able to modify it to solve tomorrow's problems (with an emphasis on tests that will prevent regressions when you modify the existing code).
These days, rather than focusing on class-level reuse, we've achieved reuse via RESTful web services (and variations thereof) as well as via open source stacks. RESTful web services are usually closed source and proprietary. However, they have a lot of benefits. For instance, they're language agnostic. It's also a lot easier to control access to a RESTful Web Service than it is to a class library. This permits good authorization controls and various monetization strategies.
As I mentioned before, another place where we see a lot of reuse is in the open source stack. Just as Taco Bell has a million things on the menu that are all made from the same 10 ingredients, there are a million startups out there all based on the same stack of open source software. We even have a word for it--LAMP. Sure, there are variations of this--PostgreSQL instead of MySQL, Nginx instead of Apache, Python and Ruby instead of PHP--however, the fact remains that a lot of startups are only possible because of the tremendous amount of code that is available for reuse.
Hence, it's clear that code reuse arrived during the last 10-20 years. It didn't come exactly as we expected, but it's definitely here.