Bjarne Stroustrup is on a mission to simplify generic programming.
In a recently published paper titled \u00a0\u00bb Concepts: The Future of Generic Programming ,\u00a0\u00bb Stroustrup makes the case for concepts as a foundation for generic programming. In concepts, Stroustrup sees the solution to the interface specification problem that has long dogged C++, the language he founded more than 35 years ago.
\u201cThe way we write generic code today is simply too different from the way we write other code,\u201d Stroustrup says.
Stroustrup defines generic programming as programming focused on design and implementation of general algorithms, with algorithms capable of accepting a variety of types. Generic programming can also be used to write efficient libraries. Stroustrup hopes to see his ideas come to fruition in C++ in fewer than three years. Concepts, Stroustrup believes, will greatly ease engineers\u2019 ability to write efficient, reliable C++ code.
Currently an ISO technical specification, concepts provide well-specified interfaces to templates without runtime overhead. Concepts, Stroustrup writes, are intended to complete C++\u2019s support for generic programming as initially envisioned. \u201cThe purpose of concepts is to fundamentally simplify and improve design. This leads to fewer bugs and clearer — often shorter — code.\u201d
The most obvious effect will be a massive improvement in the quality of error messages, but the most important long-term effect will be found in the flexibility and clarity of code, Stroustrup says. \u201cIn particular, having well-specified interfaces allows for simple, general and zero-overhead overloading of templates. That simplifies much generic code.\u201d
Concepts also address the long-standing problem of template syntax being too heavy. Stroustrup\u2019s solution will allow programmers to test the type of template arguments against user-defined compile-time predicates.
Concepts currently are available as part of GNU C Compiler 6.2. Stroustrup would like to see them be part of C++ 20.
\u201cI hope all major C++ implementations will support concepts well before 2020. IMO, concepts should have been part of C++ 17 , but the committee couldn\u2019t reach consensus on that,\u201d Stroustrup writes.
Once concepts are in the standard working paper, they can then be used to simplify the standard library and to introduce Ranges, a modernized version of the standard library featuring concepts.
Concepts are meant to complete C++\u2019s support for generic programming as initially envisioned.
Stroustrup recalls what he had in mind: \u201cI wanted three properties for templates: full generality\/expressiveness, zero overhead compared to hand coding [and] well-specified interfaces.\u201d
But no one could figure out how to get all three, so C++ ended up with Turing completeness and better-than-hand-coding performance but lousy interfaces — basically compile-time duck typing, in which a function accepts any type that has the properties that the implementation happens to use, instead of checking types in interfaces. This situation can result in complicated code.
While Stroustrup focuses on C++, his solution could be applied to other languages.
\u201cThe basic ideas are very general,\u201d Stroustrup writes. \u201cThe idea of applying a compile-time predicate can be applied to any compiled language, and many languages offer some variant of the idea.\u201d
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