CppCon 2017

Pattern matching brings a declarative approach to destructuring and inspecting complex data types. It’s a very powerful abstraction provided by many programming languages such as Haskell and OCaml, and more recently, Rust, Scala, and Swift.

We’ll see a glimpse of pattern matching in C++17 and their current limitations through features such as structured bindings, `apply`, and `visit`. We’ll then jump into MPark.Patterns, an experimental pattern matching library for C++. The following is an example of `fizzbuzz` written with the library:

void fizzbuzz() {
   for (int i = 1; i ＜= 100; ++i) {
    using namespace mpark::patterns;
    match(i % 3, i % 5)(
      pattern(0, 0) = [] { std::cout ＜＜ "fizzbuzz\n"; },
      pattern(0, _) = [] { std::cout ＜＜ "fizz\n"; },
      pattern(_, 0) = [] { std::cout ＜＜ "buzz\n"; },
      pattern(_, _) = [i] { std::cout ＜＜ i ＜＜ '\n'; });
  }
}

We’ll see many more examples like this that lead to simpler, declarative code that focuses on the desired shape/state of the data, rather than a sequence of imperative code that tries to inspect the data in piecemeal.

The goal of the library, and the talk is to gain experience and exposure to pattern matching in order to potentially help guide the design of a language-based pattern matching mechanism.