What are some of the current trends and research topics in generic programming?

1 Concepts and constraints

Concepts and constraints are the main tools for specifying the requirements and properties of generic types and functions. Concepts are abstract descriptions of the syntax and semantics of a type, such as its operations, attributes, and relations. Constraints are logical expressions that check whether a type satisfies a concept or a combination of concepts. For example, a concept could define what it means to be sortable, and a constraint could check whether a type has a comparison operator.

2 History of concepts and constraints

The idea of concepts and constraints can be traced back to the early days of generic programming, when pioneers like Alexander Stepanov and David Musser developed the Standard Template Library (STL) for C++. The STL used informal documentation and naming conventions to express the requirements and assumptions of its generic components, such as iterators, containers, and algorithms. However, this approach was not enough to ensure type safety, correctness, and clarity of generic code, and led to some problems like obscure error messages, unintended conversions, and code bloat.

3 Evolution of concepts and constraints

To address these problems, several proposals and extensions were made to introduce concepts and constraints as explicit features of the C++ language. The most notable ones were the Concepts Technical Specification (TS) in 2015, which introduced a new syntax and semantics for defining and using concepts and constraints, and the Concepts Lite proposal in 2017, which simplified and refined the TS. In 2020, C++20 finally adopted concepts and constraints as part of the standard, along with other improvements like ranges, modules, and coroutines.

4 Benefits of concepts and constraints

Concepts and constraints offer several benefits for generic programming, such as improving the readability and expressiveness of generic code with meaningful names and abstractions instead of low-level details and workarounds. They also enhance the type safety and correctness of generic code, enabling the compiler to check validity and compatibility at compile time and generate more informative error messages. Furthermore, concepts and constraints optimize the performance and efficiency of generic code by allowing the compiler to eliminate unnecessary conversions, copies, and instantiations, as well as applying more aggressive optimizations.

5 Challenges and limitations of concepts and constraints

Concepts and constraints are not a silver bullet, and they come with their own set of challenges and limitations for generic programming. For example, they can complicate the language by introducing new syntax, semantics, and rules that must be understood and followed. Designing and implementing concepts and constraints requires careful consideration of the trade-offs between generality, specificity, consistency, and compatibility. Additionally, concepts and constraints do not solve all the issues with generic programming, such as the lack of reflection or metaprogramming capabilities, or the difficulty of debugging and testing generic code.

6 Trends and topics in generic programming

Despite certain challenges and limitations, concepts and constraints have been a major milestone in the evolution of generic programming, opening up new possibilities for further research and development. Currently, topics in generic programming include exploring new domains and applications such as parallelism, concurrency, distributed systems, machine learning, or graphics; developing new tools and techniques such as libraries, frameworks, compilers, debuggers, or analyzers; and studying new theories and models such as type systems, semantics, logic, or algebra.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?