وحدات C++20

// math_utils.cppm — module interface unit
export module math_utils;    // module declaration

import <cmath>;               // import a header unit

// Exported — visible to importers
export double circle_area(double radius) {
    return std::numbers::pi * radius * radius;
}

export struct Point {
    double x, y;

    double distance_to(const Point& other) const {
        double dx = x - other.x;
        double dy = y - other.y;
        return std::sqrt(dx * dx + dy * dy);
    }
};

// NOT exported — module-private (internal linkage)
double helper_function(double val) {
    return val * val;
}

// Export a namespace — all members become visible
export namespace geometry {
    double triangle_area(double base, double height) {
        return 0.5 * base * height;
    }

    double rectangle_area(double width, double height) {
        return width * height;
    }
}

// main.cpp — imports the module
import math_utils;

#include <iostream>  // can still use #include for non-modularized headers

int main() {
    double area = circle_area(5.0);
    std::cout << "Circle area: " << area << "\n";

    Point p1{0.0, 0.0};
    Point p2{3.0, 4.0};
    std::cout << "Distance: " << p1.distance_to(p2) << "\n";  // 5.0

    std::cout << "Triangle: " << geometry::triangle_area(10, 5) << "\n";

    // helper_function(42);  // ERROR: not exported, not visible

    return 0;
}

// Compile order matters for modules:
// 1. Compile the module interface first:
//    g++ -std=c++20 -fmodules-ts -c math_utils.cppm
// 2. Then compile the consumer:
//    g++ -std=c++20 -fmodules-ts main.cpp -o main

// --- math_utils-algebra.cppm (partition interface) ---
export module math_utils:algebra;

export double square(double x) { return x * x; }
export double cube(double x) { return x * x * x; }

// --- math_utils-trig.cppm (partition interface) ---
export module math_utils:trig;

import <cmath>;

export double deg_to_rad(double degrees) {
    return degrees * std::numbers::pi / 180.0;
}

export double sin_deg(double degrees) {
    return std::sin(deg_to_rad(degrees));
}

// --- math_utils.cppm (primary module interface) ---
export module math_utils;

// Re-export partitions — consumers see everything
export import :algebra;
export import :trig;

// Additional exports can go here
export double hypotenuse(double a, double b) {
    return std::sqrt(square(a) + square(b));
}

// --- Consumer ---
// import math_utils;  // gets algebra, trig, and hypotenuse