Patternia v0.6.0 Release Note

Release Date: December 16, 2025 Version: 0.6.0

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Overview

Patternia v0.6.0 expanded the expressive range of the matcher with generic handlers, multi-value guards, and direct structural binding.

This historical page has been normalized to the current pipeline API. The original release note used the removed chained builder syntax.

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Highlights

Generic Handlers

Handlers can stay generic while still receiving correctly bound values.

using namespace ptn;

struct Matrix {
  int rows;
  int cols;
  std::vector<double> data;
};

std::string describe(const Matrix &matrix) {
  return match(matrix) | on(
    $(has<&Matrix::rows, &Matrix::cols, &Matrix::data>()) >>
        [](auto rows, auto cols, const auto &data) {
          return std::to_string(rows) + "x" + std::to_string(cols) +
                 ":" + std::to_string(data.size());
        },
    _ >> [] { return std::string("invalid"); }
  );
}

Multi-Value Guards

arg<N> made it possible to express relationships between multiple bound values.

using namespace ptn;

struct Rect {
  int width;
  int height;
};

const char *classify(const Rect &rect) {
  return match(rect) | on(
    bind(has<&Rect::width, &Rect::height>())
        [arg<0> == arg<1>] >> "square",
    bind(has<&Rect::width, &Rect::height>())
        [arg<0> > arg<1>] >> "wide",
    _ >> "other"
  );
}

Structural Binding

Binding a structural pattern forwards the selected members directly to the handler.

using namespace ptn;

struct Point {
  int x;
  int y;
};

int sum(const Point &point) {
  return match(point) | on(
    $(has<&Point::x, &Point::y>()) >> [](int x, int y) {
      return x + y;
    },
    _ >> 0
  );
}

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What Still Matters

• Generic lambdas work with Patternia's normal binding rules.
• arg<N> is the current way to write relationships across bound values.
• Binding a structural pattern is still the direct route to member extraction.

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Historical Note

The original v0.6.0 note documented the same capabilities through the old builder-style entry points. Those have since been removed; use match(subject) | on(...) in current code.