cpp / expert
Snippet
Type Erasure with Polymorphic Wrappers
Type erasure is a technique used to store objects of different types that provide a specific interface (like 'render()') without requiring them to inherit from a common base class. This is how std::function and std::any are implemented.
snippet.cpp
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#include <iostream>#include <memory>#include <vector>class Drawable {struct Concept {virtual ~Concept() = default;virtual void draw() const = 0;};template <typename T> struct Model final : Concept {Model(T x) : data(std::move(x)) {}void draw() const override { data.render(); }T data;};std::unique_ptr<Concept> self;public:template <typename T> Drawable(T x) : self(std::make_unique<Model<T>>(std::move(x))) {}void draw() const { self->draw(); }};struct Circle { void render() const { std::cout << "Circle\n"; } };int main() {std::vector<Drawable> items { Circle{} };items[0].draw();}
Breakdown
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struct Concept { ... virtual void draw() ... };
An internal abstract base class defining the required interface.
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template <typename T> struct Model : Concept { ... };
A templated wrapper that maps the generic draw() call to the specific render() method of type T.