[et] tags/separate
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6861215065
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77e5f927e7
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#include <cstdio>
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#include <tuple>
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/* **** */
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/* tags */
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namespace tag {
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struct Add;
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struct Mul;
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struct Minus;
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}
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/* ********** */
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/* expression */
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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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template<template<typename> class Evaluator>
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auto eval() const {
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return eval<Evaluator>(std::make_index_sequence<sizeof...(Operands)>{});
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}
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private:
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template<template<typename> class Evaluator, std::size_t... Is>
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auto eval(std::index_sequence<Is...>) const {
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return Evaluator<Op>::eval(std::get<Is>(_operands).template eval<Evaluator>()...);
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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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template<template<typename> class>
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auto eval() const { return _value; }
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};
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/* *********** */
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/* type traits */
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namespace impl {
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template<typename T> struct IsExpr: std::false_type {};
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template<typename Op, typename... Operands>
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struct IsExpr<Expr<Op, Operands...>>: std::true_type {};
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template<typename T>
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struct IsExpr<Value<T>>: std::true_type {};
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}
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template<typename T>
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constexpr bool IsExpr = impl::IsExpr<T>::value;
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template<
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typename LHS, typename RHS,
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std::enable_if_t<IsExpr<LHS> && IsExpr<RHS>>* = nullptr
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>
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auto operator+(LHS lhs, RHS rhs) {
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return Expr<tag::Add, LHS, RHS>{lhs, rhs};
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}
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template<
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typename LHS, typename RHS,
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std::enable_if_t<IsExpr<LHS> && IsExpr<RHS>>* = nullptr
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>
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auto operator*(LHS lhs, RHS rhs) {
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return Expr<tag::Mul, LHS, RHS>{lhs, rhs};
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}
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template<
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typename RHS,
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std::enable_if_t<IsExpr<RHS>>* = nullptr
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>
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auto operator-(RHS rhs) {
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return Expr<tag::Minus, RHS>{rhs};
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}
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/* ********** */
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/* evaluators */
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template<typename> struct EvaluatorElem;
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template<>
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struct EvaluatorElem<tag::Add> {
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template<typename T>
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static auto eval(T lhs, T rhs) { return lhs + rhs; }
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};
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template<>
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struct EvaluatorElem<tag::Mul> {
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template<typename T>
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static auto eval(T lhs, T rhs) { return lhs * rhs; }
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};
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template<>
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struct EvaluatorElem<tag::Minus> {
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template<typename T>
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static auto eval(T rhs) { return -rhs; }
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};
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/* *** */
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template<typename> struct EvaluatorBool;
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template<>
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struct EvaluatorBool<tag::Add> {
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static auto eval(bool lhs, bool rhs) { return lhs or rhs; }
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};
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template<>
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struct EvaluatorBool<tag::Mul> {
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static auto eval(bool lhs, bool rhs) { return lhs and rhs; }
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};
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template<>
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struct EvaluatorBool<tag::Minus> {
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static auto eval(bool rhs) { return not rhs; }
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};
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/* *** */
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template<template<typename> class Evaluator, typename Expr>
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auto eval(Expr expr) {
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return expr.template eval<Evaluator>();
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}
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int main() {
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int volatile v[]{1, 1, 1};
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int result;
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Value<int> v0{v[0]}, v1{v[1]}, v2{v[2]};
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auto expr = v0 * -(v1 + v2);
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result = eval<EvaluatorElem>(expr);
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std::printf("evaluator elem: %d\n", result);
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result = eval<EvaluatorBool>(expr);
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std::printf("evaluator bool: %d\n", result);
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}
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@ -0,0 +1,128 @@
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#include <cstdio>
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#include <tuple>
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/* **** */
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/* tags */
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namespace tag {
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struct Add {};
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struct Mul {};
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struct Minus {};
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}
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/* ********** */
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/* expression */
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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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template<typename Evaluator>
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auto eval() const {
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return eval<Evaluator>(std::make_index_sequence<sizeof...(Operands)>{});
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}
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private:
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template<typename Evaluator, std::size_t... Is>
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auto eval(std::index_sequence<Is...>) const {
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return Evaluator::eval(Op{}, std::get<Is>(_operands).template eval<Evaluator>()...);
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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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template<typename>
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auto eval() const { return _value; }
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};
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/* *********** */
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/* type traits */
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namespace impl {
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template<typename T> struct IsExpr: std::false_type {};
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template<typename Op, typename... Operands>
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struct IsExpr<Expr<Op, Operands...>>: std::true_type {};
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template<typename T>
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struct IsExpr<Value<T>>: std::true_type {};
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}
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template<typename T>
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constexpr bool IsExpr = impl::IsExpr<T>::value;
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template<
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typename LHS, typename RHS,
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std::enable_if_t<IsExpr<LHS> && IsExpr<RHS>>* = nullptr
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>
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auto operator+(LHS lhs, RHS rhs) {
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return Expr<tag::Add, LHS, RHS>{lhs, rhs};
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}
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template<
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typename LHS, typename RHS,
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std::enable_if_t<IsExpr<LHS> && IsExpr<RHS>>* = nullptr
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>
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auto operator*(LHS lhs, RHS rhs) {
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return Expr<tag::Mul, LHS, RHS>{lhs, rhs};
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}
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template<
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typename RHS,
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std::enable_if_t<IsExpr<RHS>>* = nullptr
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>
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auto operator-(RHS rhs) {
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return Expr<tag::Minus, RHS>{rhs};
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}
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/* ********** */
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/* evaluators */
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struct EvaluatorElem {
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template<typename T>
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static auto eval(tag::Add, T lhs, T rhs) { return lhs + rhs; }
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template<typename T>
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static auto eval(tag::Mul, T lhs, T rhs) { return lhs * rhs; }
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template<typename T>
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static auto eval(tag::Minus, T rhs) { return -rhs; }
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};
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struct EvaluatorBool {
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static auto eval(tag::Add, bool lhs, bool rhs) { return lhs or rhs; }
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static auto eval(tag::Mul, bool lhs, bool rhs) { return lhs and rhs; }
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static auto eval(tag::Minus, bool rhs) { return not rhs; }
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};
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/* *** */
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template<typename Evaluator, typename Expr>
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auto eval(Expr expr) {
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return expr.template eval<Evaluator>();
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}
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int main() {
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int volatile v[]{1, 1, 1};
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int result;
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Value<int> v0{v[0]}, v1{v[1]}, v2{v[2]};
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auto expr = v0 * -(v1 + v2);
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result = eval<EvaluatorElem>(expr);
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std::printf("evaluator elem: %d\n", result);
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result = eval<EvaluatorBool>(expr);
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std::printf("evaluator bool: %d\n", result);
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}
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