130 lines
2.9 KiB
C++
130 lines
2.9 KiB
C++
// Copyright (C) 2016-2018 T. Zachary Laine
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//
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// Distributed under the Boost Software License, Version 1.0. (See
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// accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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//[ vec3
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#include <boost/yap/yap.hpp>
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#include <array>
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#include <iostream>
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struct take_nth
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{
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auto operator() (boost::yap::terminal<boost::yap::expression, std::array<int, 3>> const & expr)
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{
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int x = boost::yap::value(expr)[n];
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// The move forces the terminal to store the value of x, not a
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// reference.
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return boost::yap::make_terminal(std::move(x));
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}
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std::size_t n;
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};
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// Since this example doesn't constrain the operators defined on its
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// expressions, we can just use boost::yap::expression<> as the expression
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// template.
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using vec3_terminal = boost::yap::expression<
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boost::yap::expr_kind::terminal,
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boost::hana::tuple<std::array<int, 3>>
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>;
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// Customize the terminal type we use by adding index and assignment
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// operations.
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struct vec3 : vec3_terminal
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{
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explicit vec3 (int i = 0, int j = 0, int k = 0)
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{
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(*this)[0] = i;
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(*this)[1] = j;
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(*this)[2] = k;
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}
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explicit vec3 (std::array<int, 3> a)
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{
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(*this)[0] = a[0];
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(*this)[1] = a[1];
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(*this)[2] = a[2];
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}
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int & operator[] (std::ptrdiff_t i)
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{ return boost::yap::value(*this)[i]; }
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int const & operator[] (std::ptrdiff_t i) const
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{ return boost::yap::value(*this)[i]; }
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template <typename T>
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vec3 & operator= (T const & t)
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{
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decltype(auto) expr = boost::yap::as_expr(t);
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(*this)[0] = boost::yap::evaluate(boost::yap::transform(expr, take_nth{0}));
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(*this)[1] = boost::yap::evaluate(boost::yap::transform(expr, take_nth{1}));
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(*this)[2] = boost::yap::evaluate(boost::yap::transform(expr, take_nth{2}));
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return *this;
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}
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void print() const
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{
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std::cout << '{' << (*this)[0]
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<< ", " << (*this)[1]
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<< ", " << (*this)[2]
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<< '}' << std::endl;
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}
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};
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// This is a stateful transform that keeps a running count of the terminals it
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// has seen.
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struct count_leaves_impl
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{
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auto operator() (vec3_terminal const & expr)
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{
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value += 1;
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return expr;
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}
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int value = 0;
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};
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template <typename Expr>
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int count_leaves (Expr const & expr)
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{
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count_leaves_impl impl;
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boost::yap::transform(boost::yap::as_expr(expr), impl);
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return impl.value;
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}
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int main()
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{
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vec3 a, b, c;
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c = 4;
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b[0] = -1;
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b[1] = -2;
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b[2] = -3;
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a = b + c;
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a.print();
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vec3 d;
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auto expr1 = b + c;
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d = expr1;
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d.print();
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int num = count_leaves(expr1);
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std::cout << num << std::endl;
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num = count_leaves(b + 3 * c);
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std::cout << num << std::endl;
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num = count_leaves(b + c * d);
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std::cout << num << std::endl;
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return 0;
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}
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//]
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