62 lines
1.1 KiB
C++
62 lines
1.1 KiB
C++
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#include <cstdio>
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#include <tuple>
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/* unchanged from et/1_first_draft.cpp */
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struct Add {
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template<typename T>
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static auto eval(T lhs, T rhs) {
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return lhs + rhs;
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}
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};
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struct Mul {
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template<typename T>
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static auto eval(T lhs, T rhs) {
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return lhs * rhs;
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}
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};
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template<typename T>
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class Value {
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T _value;
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public:
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Value(T value): _value(value) {}
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auto eval() const { return _value; }
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};
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/* end of unchanged */
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template<typename Op, typename... Operands>
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class Expr {
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std::tuple<Operands...> _operands;
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public:
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Expr(Operands... operands): _operands{operands...} {}
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auto eval() const {
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return eval(std::make_index_sequence<sizeof...(Operands)>{});
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}
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private:
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template<std::size_t... Is>
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auto eval(std::index_sequence<Is...>) const {
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return Op::eval(std::get<Is>(_operands).eval()...);
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}
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};
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/* unchanged from et/1_first_draft.cpp */
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int main() {
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using SubExpr = Expr<Mul, Value<int>, Value<int>>;
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using MyExpr = Expr<Add, Value<int>, SubExpr>;
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int volatile v0 = 3, v1 = 5, v2 = 7;
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int result;
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MyExpr expr{{v0}, {{v1}, {v2}}};
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result = expr.eval();
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std::printf("%d\n", result);
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}
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/* end of unchanged */
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