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// Copyright (C) 2016-2018 T. Zachary Laine
//
// Distributed under the Boost Software License, Version 1.0. (See
// accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
//[ tarray
#include <boost/yap/algorithm.hpp>
#include <boost/yap/print.hpp>
#include <array>
#include <iostream>
template <boost::yap::expr_kind Kind, typename Tuple>
struct tarray_expr;
struct take_nth
{
boost::yap::terminal<tarray_expr, int>
operator() (boost::yap::terminal<tarray_expr, std::array<int, 3>> const & expr);
std::size_t n;
};
// Another custom expression template. In this case, we static_assert() that
// it only gets instantiated with terminals with pre-approved value types.
template <boost::yap::expr_kind Kind, typename Tuple>
struct tarray_expr
{
// Make sure that, if this expression is a terminal, its value is one we
// want to support. Note that the presence of expr_kind::expr_ref makes
// life slightly more difficult; we have to account for int const & and
// int & as well as int.
static_assert(
Kind != boost::yap::expr_kind::terminal ||
std::is_same<Tuple, boost::hana::tuple<int const &>>{} ||
std::is_same<Tuple, boost::hana::tuple<int &>>{} ||
std::is_same<Tuple, boost::hana::tuple<int>>{} ||
std::is_same<Tuple, boost::hana::tuple<std::array<int, 3>>>{},
"tarray_expr instantiated with an unsupported terminal type."
);
static const boost::yap::expr_kind kind = Kind;
Tuple elements;
int operator[] (std::size_t n) const
{ return boost::yap::evaluate(boost::yap::transform(*this, take_nth{n})); }
};
// Define operators +, -, *, and /.
BOOST_YAP_USER_BINARY_OPERATOR(plus, tarray_expr, tarray_expr)
BOOST_YAP_USER_BINARY_OPERATOR(minus, tarray_expr, tarray_expr)
BOOST_YAP_USER_BINARY_OPERATOR(multiplies, tarray_expr, tarray_expr)
BOOST_YAP_USER_BINARY_OPERATOR(divides, tarray_expr, tarray_expr)
boost::yap::terminal<tarray_expr, int>
take_nth::operator() (boost::yap::terminal<tarray_expr, std::array<int, 3>> const & expr)
{
int x = boost::yap::value(expr)[n];
// Again, this is the move hack to get x into the resulting terminal as a
// value instead of a reference.
return boost::yap::make_terminal<tarray_expr>(std::move(x));
}
// Stream-out operators for the two kinds of terminals we support.
std::ostream & operator<< (std::ostream & os, boost::yap::terminal<tarray_expr, int> expr)
{ return os << '{' << boost::yap::value(expr) << '}'; }
std::ostream & operator<< (std::ostream & os, boost::yap::terminal<tarray_expr, std::array<int, 3>> expr)
{
std::array<int, 3> const & a = boost::yap::value(expr);
return os << '{' << a[0] << ", " << a[1] << ", " << a[2] << '}';
}
// Stream-out operators for general expressions. Note that we have to treat
// the reference case separately; this also could have been done using
// constexpr if in a single function template.
template <typename Tuple>
std::ostream & operator<< (std::ostream & os, tarray_expr<boost::yap::expr_kind::expr_ref, Tuple> const & expr)
{ return os << boost::yap::deref(expr); }
template <boost::yap::expr_kind Kind, typename Tuple>
std::ostream & operator<< (std::ostream & os, tarray_expr<Kind, Tuple> const & expr)
{
if (Kind == boost::yap::expr_kind::plus || Kind == boost::yap::expr_kind::minus)
os << '(';
os << boost::yap::left(expr) << " " << op_string(Kind) << " " << boost::yap::right(expr);
if (Kind == boost::yap::expr_kind::plus || Kind == boost::yap::expr_kind::minus)
os << ')';
return os;
}
// Since we want different behavior on terminals than on other kinds of
// expressions, we create a custom type that does so.
struct tarray :
tarray_expr<
boost::yap::expr_kind::terminal,
boost::hana::tuple<std::array<int, 3>>
>
{
explicit tarray (int i = 0, int j = 0, int k = 0)
{
(*this)[0] = i;
(*this)[1] = j;
(*this)[2] = k;
}
explicit tarray (std::array<int, 3> a)
{
(*this)[0] = a[0];
(*this)[1] = a[1];
(*this)[2] = a[2];
}
int & operator[] (std::ptrdiff_t i)
{ return boost::yap::value(*this)[i]; }
int const & operator[] (std::ptrdiff_t i) const
{ return boost::yap::value(*this)[i]; }
template <typename T>
tarray & operator= (T const & t)
{
// We use as_expr() here to make sure that the value passed to
// assign() is an expression. as_expr() simply forwards expressions
// through, and wraps non-expressions as terminals.
return assign(boost::yap::as_expr< ::tarray_expr>(t));
}
template <typename Expr>
tarray & printAssign (Expr const & expr)
{
*this = expr;
std::cout << *this << " = " << expr << std::endl;
return *this;
}
private:
template <typename Expr>
tarray & assign (Expr const & expr)
{
(*this)[0] = expr[0];
(*this)[1] = expr[1];
(*this)[2] = expr[2];
return *this;
}
};
int main()
{
tarray a(3,1,2);
tarray b;
std::cout << a << std::endl;
std::cout << b << std::endl;
b[0] = 7; b[1] = 33; b[2] = -99;
tarray c(a);
std::cout << c << std::endl;
a = 0;
std::cout << a << std::endl;
std::cout << b << std::endl;
std::cout << c << std::endl;
a = b + c;
std::cout << a << std::endl;
a.printAssign(b+c*(b + 3*c));
return 0;
}
//]
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