Add 'old_style_generator.cpp'

old_style_generator.cpp

@@ -0,0 +1,74 @@
+#include <iostream>
+
+template<typename result, typename state_t>
+struct Generator {
+    typedef state_t(*initializer_t)();
+    typedef state_t(*advancer_t)(state_t&&);
+    typedef result(*extractor_t)(state_t&);
+    state_t state;
+    initializer_t initializer;
+    advancer_t advancer;
+    extractor_t extractor;
+    Generator(
+        initializer_t init,
+        advancer_t adv,
+        extractor_t extr
+    )
+    : state{init()}
+    , initializer{init}
+    , advancer{adv}
+    , extractor{extr}
+    {}
+
+    bool next() {
+        state = advancer(std::move(state));
+        return static_cast<bool>(state);
+    }
+
+    result value() {
+        return extractor(state);
+    }
+
+    void reset() {
+        state = initializer();
+    }
+
+    operator bool() { return static_cast<bool>(state); }
+};
+
+struct int_advance_state {
+    int current;
+    bool done;
+
+    operator bool() const {
+        return !done;
+    }
+};
+
+int_advance_state init() {
+    return {0, false};
+}
+
+int_advance_state advancer(int_advance_state&& prev) {
+    if (static_cast<bool>(prev)) return {prev.current + 1, prev.current >= 10};
+    return {0, true};
+}
+
+int extractor(int_advance_state& prev) {
+    return prev.current;
+}
+
+int main() {
+    Generator<int, int_advance_state> gen{
+        init, 
+        advancer, 
+        extractor
+    };
+
+    while (gen) {
+        std::cout << gen.value() << std::endl;
+        gen.next();
+    }
+
+    return 0;
+}