The Shape of Code

How often are the features supported by a programming language used by developers in the code that they write?

This fundamental question is rarely asked, let alone answered (my contribution).

Existing code is what developers spend their time reading, compilers translating to machine code, and LLMs use as training data.

Frequently used language features are of interest to writers of code optimizers, who want to know where to focus their limited resources (at least I did when I was involved in the optimization business; I was always surprised by others working in the field having almost no interest in measuring user’s code), and educators ought to be interested in teaching what students are mostly likely to be using (rather than teaching the features that are fun to talk about).

The unused, or rarely used language features are also of interest. Is the feature rarely used because developers have no use for the feature, or does its semantics prevent it being practically applied, or some other reason?

Language designers write books, papers, and blog posts discussing their envisaged developer usage of each feature, and how their mental model of the language ties everything together to create a unifying whole; measurements of actual source code very rarely get discussed. Two very interesting reads in this genre are Stroustrup’s The Design and Evolution of C++ and Thriving in a Crowded and Changing World: C++ 2006–2020.

Languages with an active user base are often updated to support new features. The ISO C++ committee is aims to release a new standard every three years, Java is now on a six-month release cycle, and Python has an annual release cycle. The primary incentives driving the work needed to create these updates appears to be:

• sales & marketing: saturation exposure to adverts proclaiming modernity has warped developer perception of programming languages, driving young developers to want to be associated with those perceived as modern. Companies need to hire inexperienced developers (who are likely still running on the modernity treadmill), and appearing out of date can discourage developers from applying for a job,
• designer hedonism and fuel for the trainer/consultant gravy train: people create new programming languages because it’s something they enjoy doing; some even leave their jobs to work on their language full-time. New language features provides material to talk about and income opportunities for trainers/consultants.

Note: I’m not saying that adding new features to a language is bad, but that at the moment worthwhile practical use to developers is a marketing claim rather than an evidence-based calculation.

Those proposing new language features can rightly point out that measuring language usage is a complicated process, and that it takes time for new features to diffuse into developers’ repertoire. Also, studying source code measurement data is not something that appeals to many people.

Also, the primary intended audience for some language features is library implementors, e.g., templates.

There have been some studies of language feature usage. Lambda expressions are a popular research subject, having been added as a new feature to many languages, e.g., C++, Java, and Python. A few papers have studied language usage in specific contexts, e.g., C++ new feature usage in KDE.

The number of language features invariably grow and grow. Sometimes notice is given that a feature will be removed from a future reversion of the language. Notice of feature deprecation invariably leads to developer pushback by the subset of the community that relies on that feature (measuring usage would help prevent embarrassing walk backs).

If the majority of newly written code does end up being created by developers prompting LLMs, then new language features are unlikely ever to be used. Without sufficient training data, which comes from developers writing code using the new features, LLMs are unlikely to respond with code containing new features.

I am not expecting the current incentive structure to change.