Patternia

Patternia: A High-Performance Pattern Matching Library for Modern C++

Patternia is a header-only, zero-overhead library dedicated to enabling pattern matching capabilities in modern C++. It acts as a transformative mechanism, allowing developers to express branching logic in a more declarative and maintainable manner, improving the management of complex control flows.

What Is Pattern Matching?

Pattern matching is a sophisticated control-flow mechanism that selects execution paths based on the structural form or type of values. By integrating discrimination, decomposition, and structured binding, it encourages a conceptual understanding of data shapes as opposed to traditional conditional statements like if-else or switch. This approach not only enhances readability but also fosters clearer reasoning about data.

Why Use Patternia?

Patternia addresses several longstanding challenges in C++ related to control flows and data-oriented logic:

1. Organized Control Logic

With conventional approaches, control flow typically relies on scattered logic combining type checks and nested conditionals. For instance,

if (value is TypeA) {  
    // logic for TypeA  
} else if (value is TypeB) {  
    // logic for TypeB  
}  

Patternia enables control flow organization around data structures, making it clearer and more manageable:

match value {  
    when PatternA(x) => { /* logic for PatternA */ }  
    when PatternB(y) => { /* logic for PatternB */ }  
    otherwise => { /* fallback case */ }  
}  

This ensures each condition is explicit regarding the expected data structure.

2. Separation of Concerns

Patternia separates decomposition from conditional checks, enhancing readability and comprehension. Using patterns to express the decomposition of data:

match(p)  
  .when(bind(has<&Point::x, &Point::y>())) >> [](int x, int y) {  
      /* operate on x and y */  
  }  
.otherwise(...);  

This helps maintain clarity, especially as conditions grow complex.

3. Enhanced Guard Functionality

Patternia introduces first-class guard expressions that are composable, expressive, and structurally aware, handling relationships between multiple data fields elegantly:

match(x)  
  .when(bind()[_ > 0 && _ < 10] >> [](int v) {  
      /* process v */  
  })  
  .otherwise([] {  
      /* fallback logic */  
  });  

The guards enhance flexibility and logic structuring.

4. Unified Branching Mechanisms

Patternia provides a cohesive framework for different branching methods in C++, allowing for uniformity in a single model that incorporates various match types, enhancing overall code quality and maintainability.

5. Expression-Oriented Control Flow

Patternia treats pattern matching as an expression rather than just a control-flow statement, allowing for cleaner and more readable code:

auto result = match(n)  
  .when(lit(0) >> 0)  
  .otherwise([] { return compute(); });  

This complies with C++’s zero-overhead principle while maximizing performance through templates and inlined calls.

6. Focused on Data Shape

Patternia elevates data structure understanding in control flow, making it ideal for applications such as state machines, protocol handling, geometric logic, AST processing, and rule-based systems.

Getting Started

Integrating Patternia is straightforward due to its header-only nature, supporting modern C++ (C++17 or later). Whether utilizing CMake or other package managers, implementing Patternia enhances project robustness and code clarity. For exemplary usage, refer to the provided code snippets in the README.

Documentation & Contribution

For more extensive information regarding the API, examples, or contribution guidelines, please refer to the Patternia Documentation. Contributions in the form of bug reports or feature proposals are always welcome.

Elevate C++ control flow with Patternia—where data shape meets expressive code.