Concepts versus SFINAE-based constraints

In some situations, we need to makes sure function templates can only be invoked with some specific types. SFINAE (that stands for Substitution Failure Is Not An Error) is a set of rules that specify how compilers can discard specializations from the overload resolution without causing errors. A way to achieve this is with the help of std::enable_if.

C++20 Concepts in Visual Studio 2019 16.3 Preview 2

Back in mid-August, Microsoft released the 2nd preview of Visual Studio 2019 16.3. This is the first version of Visual Studio to support concepts from C++20 both in the compiler and the standard library (header <concepts>) without the changes made at the ISO C++ standards meeting in Cologne. These changes are available when you compile with the /std:c++latest switch.

Concepts allow performing compile-time validation of template arguments and function dispatch based on properties of types. Concepts are very useful in libraries where they can be used to impose compile-time checks on the template arguments of functions or types. For instance, a generic algorithm for sorting a container would require the container type to be sortable for the program to even compile.

In this article, I will show an example with a concept that verifies that a type T can be converted to a std::string via a to_string() function, that is either a member of the class or a free function.

C++17 standard a major… disappointment

C++17 was supposed to be a major update of the C++ ISO standard. After the Jacksonville meeting (29.02 – 05.03) it looks like it’s rather going to be a major disappointment. I’m not trying to downplay the things that have been voted into the C++17 standard so far, but all major features we hoped for…

Concepts are out of C++0x

Concepts were supposed to be an important new feature in C++0x. They were meant to allow programmers to specify properties (like constraints) for templates, allow compilers to do some optimization and tools to do some formal checking on the code. After years of debate, the standard committee found them “untried, risky and controversial” and ruled…