Functional programming is influencing everything—even C++.
Pattern matching is a clean and expressive way to check a value against a given structure or pattern. Pattern matching provides developers with a compact way to define their search criteria and specify actions for successful matches. Pattern matching unifies conditionals, destructuring, and type checks into a single, expressive construct.
Functional programming started as an academic concept for niche languages, yet it has successfully entered the general programming landscape. The adoption of functional programming concepts has spread across all programming paradigms, including Java, JavaScript, and C++.
Pattern matching, once a hallmark of purely functional languages, has now become one of the most widely adopted features, demonstrating just how far functional programming ideas have permeated mainstream languages like C++.
The C++ programming language provides developers with three methods to achieve pattern matching through std::variant, std::visit, and Mach7 as a third-party library. The current approaches for pattern matching in C++ may produce verbose code that lacks consistency and intuitive understanding when compared to native pattern-matching languages.
So here’s the real question: Should C++ fully embrace functional programming constructs like built-in pattern matching? Or should it stay true to its performance-first roots and resist this shift?
Let’s dig in.
Table of Contents
What is pattern matching?
Pattern matching is a programming construct that allows you to test data against a set of conditions—or patterns—and execute code based on which pattern fits. It’s widely used in functional programming languages like Haskell, Rust, Scala, and even modern JavaScript (via destructuring).
At a glance, pattern matching goes beyond traditional if-else or switch statements. It lets you match not just values, but also types, structures, and shapes of data—and automatically extract components as part of the process.
For example, in Rust:
enum Shape {
Circle(f64),
Square(f64),
}
fn area(shape: Shape) -> f64 {
match shape {
Shape::Circle(r) => 3.14 * r * r,
Shape::Square(s) => s * s,
}
}
This kind of code is declarative and concise. You’re not manually checking conditions—you’re saying “if it looks like this, do that.”
When to use pattern matching: think about your code in terms of “if the data structure is like this, then I want it to do this”
Key advantages of pattern matching:
- Readability: It’s easier to understand intent when logic follows natural data structures.
- Concise Code: Reduces boilerplate, especially for condition-heavy logic.
- Type Safety: Many functional languages perform exhaustive checks to ensure all possible patterns are handled, helping prevent runtime errors.
- Built-in Destructuring: You can directly extract data from complex structures in the match itself.
In short, pattern matching is about writing cleaner, safer, and more expressive code. The question is—how well does this fit into C++’s existing model?
Let’s see what C++ currently offers.
Pattern matching in C++ today
C++ doesn’t yet have built-in pattern matching in the same way languages like Rust or Haskell do, but developers have long used alternatives to achieve similar results.
Traditional approaches
Historically, C++ developers have relied on combinations of switch, if/else, and polymorphism via virtual functions to manage conditional logic.
Example using switch:
int x = 2;
switch (x) {
case 1:
std::cout << “One\n”;
break;
case 2:
std::cout << “Two\n”;
break;
default:
std::cout << “Other\n”;
}
While effective for simple values, this method doesn’t scale well to complex or variant-based data types.
Modern alternatives in C++
1. std::variant + std::visit (C++17)
With the introduction of std::variant, C++ gained a way to store one value out of a fixed set of types, similar to Rust’s enum. Pattern-like behavior can be achieved using std::visit.
Example:
#include <variant>
#include <iostream>
std::variant<int, double> data = 3.14;
std::visit([](auto&& value) {
std::cout << “Value: ” << value << “\n”;
}, data);
This approach allows for type-safe handling of different alternatives, though the syntax can be verbose for complex use cases.
2. if constexpr (C++17)
if constexpr enables compile-time conditional branching, allowing decisions based on template parameters. It’s especially useful in generic code.
Example:
template<typename T>
void printType(T value) {
if constexpr (std::is_integral<T>::value) {
std::cout << “Integral: ” << value << “\n”;
} else if constexpr (std::is_floating_point<T>::value) {
std::cout << “Floating point: ” << value << “\n”;
} else {
std::cout << “Other type\n”;
}
}
This is a form of type pattern matching evaluated at compile time.
3. Structured Bindings (C++17)
Structured bindings allow destructuring complex objects into individual components, somewhat like matching the shape of data.
Example:
std::pair<int, int> point = {3, 4};
auto [x, y] = point;
std::cout << “X: ” << x << “, Y: ” << y << “\n”;
While not pattern matching in itself, this feature improves readability and integrates well with manual matching logic.
Although C++ doesn’t yet support native pattern matching, developers can simulate it using tools from modern C++. These approaches are powerful, but not always elegant, which raises the question: Should C++ introduce native support?
Let’s look at how third-party libraries and upcoming proposals are taking things further.
C++ libraries that support pattern matching
While native pattern matching is still under consideration for future versions of C++, several third-party libraries and proposals already offer powerful ways to simulate or implement it today.
1. Mach7 (Multiple-Dispatch Pattern Matching for C++)
Mach7 is a lightweight library that brings functional-style pattern matching to C++. It supports value patterns, type patterns, guard conditions, and even open patterns, mimicking constructs from functional languages like Haskell or OCaml.
Example:
#include <iostream>
#include “match.hpp” // Mach7 header
using namespace mch;
struct Shape { virtual ~Shape() = default; };
struct Circle : Shape { double r; };
struct Square : Shape { double s; };
void describe(Shape* shape) {
Match(shape)
{
Case(Circle* c) std::cout << “Circle with radius ” << c->r << “\n”;
Case(Square* s) std::cout << “Square with side ” << s->s << “\n”;
Otherwise(std::cout << “Unknown shape\n”);
}
EndMatch
}
This syntax provides a clear, declarative way to handle multiple types, much like match statements in Rust or Scala.
2. C++ Pattern matching TS (Technical Specification)
C++ standardization efforts have proposed several enhancements to introduce pattern matching directly into the language. One such proposal is P1371R3, which introduces a match expression similar to those found in functional languages.
While still in the proposal phase, it’s a sign that the C++ community is actively exploring native support. If accepted, future C++ versions (possibly C++26) could feature syntax like:
match (value) {
case 0: std::cout << “Zero\n”; break;
case 1: std::cout << “One\n”; break;
case auto x if (x > 1): std::cout << “Greater than one\n”; break;
}
3. Boost.Hana
Boost.Hana is a metaprogramming library for compile-time computations using modern C++ features. While not a pattern-matching library per se, it enables matching patterns at compile time, making it useful for highly generic or constexpr-heavy designs.
Example (simplified):
#include <boost/hana.hpp>
namespace hana = boost::hana;
auto result = hana::if_(hana::bool_c<true>,
[]{ return “matched true”; },
[]{ return “matched false”; }
);
std::cout << result() << “\n”; // matched true
It’s more complex but powerful for metaprogramming scenarios where performance and type safety are critical.
These tools bring C++ closer to the expressive power of functional languages, sometimes at the cost of verbosity or complexity. Up next, we’ll weigh the pros and cons of fully embracing functional constructs like these in the core language itself.
The case for embracing functional constructs
Modern C++ has come a long way from its purely procedural roots. As software complexity grows, there’s a strong case to be made for adopting more functional programming constructs, with pattern matching leading the charge.
Pros of integrating pattern matching in C++
Increased expressiveness
Pattern matching lets developers express logic more clearly and concisely. Instead of juggling multiple if-else or switch statements, you can represent intent directly, making your code more intuitive and aligned with how we reason about data.
Safer and more declarative code
In languages like Rust or Haskell, pattern matching often forces you to handle all possible cases—a feature known as exhaustiveness checking. This reduces the chances of missing edge cases or encountering runtime errors due to unhandled types or values.
Alignment with modern language trends
Languages such as Rust, Scala, Kotlin, and even newer versions of Java and JavaScript are embracing pattern matching to simplify complex branching logic. For C++ to remain competitive and developer-friendly, adopting similar paradigms is a natural evolution.
How pattern matching benefits real C++ workflows
Pattern matching isn’t just about syntax sugar—it has real utility in domains where C++ already shines:
- Abstract Syntax Trees (ASTs): In compilers or interpreters, pattern matching makes it easier to traverse and manipulate tree-like structures based on node types.
- Rule Engines: Defining and applying transformation or validation rules becomes clearer when conditions can be matched declaratively.
- Embedded Systems and Finite State Machines: Handling states and transitions using pattern-based constructs can reduce bugs and improve maintainability.
In all these cases, integrating pattern matching results in less boilerplate, cleaner control flow, and more robust logic, without sacrificing C++’s performance edge.
The case against (or cautions)
While pattern matching brings many benefits, it’s important to consider the potential trade-offs, especially in a language like C++ that has always favored performance, control, and minimalism.
C++ philosophy: performance over abstraction
C++ was designed with zero-cost abstractions in mind. Features are only added when they offer clear advantages without incurring runtime overhead. Some argue that pattern matching—especially if misused—could introduce abstraction layers that compromise performance or transparency.
Compilation overhead and learning curve
Adding a native match construct could make compile times longer and error messages harder to decipher, especially when templates, lambdas, and concepts are involved. It also increases the cognitive load for newcomers, who already face a steep learning curve with C++’s complex syntax and paradigms.
Risk of bloated language design
C++ already suffers from being “feature-rich to a fault.” Critics worry that pattern matching, while elegant in theory, might become another overloaded mechanism that interacts unpredictably with templates, operator overloading, and legacy code.
Existing features already offer workarounds
Modern C++ offers several ways to simulate pattern matching, such as std::variant, std::visit, if constexpr, and structured bindings. While not perfect, these tools give developers flexibility without needing entirely new syntax or semantics.
In summary, while pattern matching could elevate C++ expressiveness, it also raises valid concerns about complexity, compilation cost, and philosophical fit. The real challenge is finding a balance between innovation and the core identity of the language.
Let’s now explore where things might be heading in the future.
What’s coming in the future? (C++23/C++26)
The future of pattern matching in C++ lies in the hands of ongoing proposals and community discussions, many of which aim to bring functional-style constructs to the language without sacrificing C++’s core principles.
Proposals in progress
One of the most notable efforts is P1371R3, which proposes a native match statement—conceptually similar to pattern matching in Rust or Scala. This construct would allow developers to match on values, types, and even conditions within a clean, expressive syntax.
The goal is to make pattern matching:
- Type-safe and exhaustive
- Compatible with C++’s type system
- Composable with other modern C++ features like std::variant, structured bindings, and concepts
Other discussions also explore integrating guards, binding patterns, and OR patterns, inspired by the rich semantics found in functional languages.
Current status and community debate
As of now:
- Pattern matching was not included in C++23.
- It’s being actively explored for C++26, but nothing is finalized.
- Some developers are excited about the direction, citing improved expressiveness and readability.
- Others are cautious, warning about language bloat, increased compiler complexity, and overlap with existing features like if constexpr and std::visit.
The C++ standards committee continues to gather feedback, refine syntax models, and weigh the impact of such a feature on both new and existing codebases.
In short, pattern matching is on C++’s radar, and the road ahead looks promising—but cautious. Whether it makes it into the official standard depends on community consensus and the committee’s vision for the language’s evolution.
Final verdict: Should C++ embrace it?
Pattern matching in C++ is no longer just a theoretical discussion—it’s a real, evolving conversation within the community. Let’s briefly revisit the key points on both sides.
The pros:
- Enhances expressiveness and readability of complex branching logic.
- Enables safer, declarative code, particularly with exhaustiveness checking.
- Aligns C++ with modern language trends, helping attract newer generations of developers.
The cons:
- Introduces potential language bloat and adds another abstraction layer.
- Increases compiler complexity and learning curve for beginners.
- Current features like std::variant, if constexpr, and libraries like Mach7 already offer viable workarounds.
So, should C++ embrace pattern matching?
The answer depends on your perspective:
- If you prioritize expressiveness, maintainability, and modern design, then native pattern matching would be a welcome step forward.
- If you value minimalism, raw performance, and avoiding abstraction, the existing tools may already meet your needs.
In either case, the growing support for pattern matching, through libraries and proposals, signals a shift in how C++ is evolving. Whether adopted in C++26 or later, the feature will likely continue to shape discussions around language design and developer ergonomics.
What do you think?
Do you want to see native pattern matching in C++? Or do you prefer the language to stay lean and low-level?
Share your thoughts in the comments. Let’s keep the discussion going!
