libs/ratio/example/si_physics.cpp
// ratio_test.cpp ----------------------------------------------------------//
// Copyright 2008 Howard Hinnant
// Copyright 2008 Beman Dawes
// Distributed under the Boost Software License, Version 1.0.
// See http://www.boost.org/LICENSE_1_0.txt
#include <iostream>
#include <boost/ratio/ratio.hpp>
#include "duration.hpp"
namespace User1
{
// Example type-safe "physics" code interoperating with chrono::duration types
// and taking advantage of the std::ratio infrastructure and design philosophy.
// length - mimics chrono::duration except restricts representation to double.
// Uses boost::ratio facilities for length units conversions.
template <class Ratio>
class length
{
public:
typedef Ratio ratio;
private:
double len_;
public:
length() : len_(1) {}
length(const double& len) : len_(len) {}
// conversions
template <class R>
length(const length<R>& d)
: len_(d.count() * boost::ratio_divide<Ratio, R>::type::den /
boost::ratio_divide<Ratio, R>::type::num) {}
// observer
double count() const {return len_;}
// arithmetic
length& operator+=(const length& d) {len_ += d.count(); return *this;}
length& operator-=(const length& d) {len_ -= d.count(); return *this;}
length operator+() const {return *this;}
length operator-() const {return length(-len_);}
length& operator*=(double rhs) {len_ *= rhs; return *this;}
length& operator/=(double rhs) {len_ /= rhs; return *this;}
};
// Sparse sampling of length units
typedef length<boost::ratio<1> > meter; // set meter as "unity"
typedef length<boost::centi> centimeter; // 1/100 meter
typedef length<boost::kilo> kilometer; // 1000 meters
typedef length<boost::ratio<254, 10000> > inch; // 254/10000 meters
// length takes ratio instead of two integral types so that definitions can be made like so:
typedef length<boost::ratio_multiply<boost::ratio<12>, inch::ratio>::type> foot; // 12 inchs
typedef length<boost::ratio_multiply<boost::ratio<5280>, foot::ratio>::type> mile; // 5280 feet
// Need a floating point definition of seconds
typedef boost_ex::chrono::duration<double> seconds; // unity
// Demo of (scientific) support for sub-nanosecond resolutions
typedef boost_ex::chrono::duration<double, boost::pico> picosecond; // 10^-12 seconds
typedef boost_ex::chrono::duration<double, boost::femto> femtosecond; // 10^-15 seconds
typedef boost_ex::chrono::duration<double, boost::atto> attosecond; // 10^-18 seconds
// A very brief proof-of-concept for SIUnits-like library
// Hard-wired to floating point seconds and meters, but accepts other units (shown in testUser1())
template <class R1, class R2>
class quantity
{
double q_;
public:
typedef R1 time_dim;
typedef R2 distance_dim;
quantity() : q_(1) {}
double get() const {return q_;}
void set(double q) {q_ = q;}
};
template <>
class quantity<boost::ratio<1>, boost::ratio<0> >
{
double q_;
public:
quantity() : q_(1) {}
quantity(seconds d) : q_(d.count()) {} // note: only User1::seconds needed here
double get() const {return q_;}
void set(double q) {q_ = q;}
};
template <>
class quantity<boost::ratio<0>, boost::ratio<1> >
{
double q_;
public:
quantity() : q_(1) {}
quantity(meter d) : q_(d.count()) {} // note: only User1::meter needed here
double get() const {return q_;}
void set(double q) {q_ = q;}
};
template <>
class quantity<boost::ratio<0>, boost::ratio<0> >
{
double q_;
public:
quantity() : q_(1) {}
quantity(double d) : q_(d) {}
double get() const {return q_;}
void set(double q) {q_ = q;}
};
// Example SI-Units
typedef quantity<boost::ratio<0>, boost::ratio<0> > Scalar;
typedef quantity<boost::ratio<1>, boost::ratio<0> > Time; // second
typedef quantity<boost::ratio<0>, boost::ratio<1> > Distance; // meter
typedef quantity<boost::ratio<-1>, boost::ratio<1> > Speed; // meter/second
typedef quantity<boost::ratio<-2>, boost::ratio<1> > Acceleration; // meter/second^2
template <class R1, class R2, class R3, class R4>
quantity<typename boost::ratio_subtract<R1, R3>::type, typename boost::ratio_subtract<R2, R4>::type>
operator/(const quantity<R1, R2>& x, const quantity<R3, R4>& y)
{
typedef quantity<typename boost::ratio_subtract<R1, R3>::type, typename boost::ratio_subtract<R2, R4>::type> R;
R r;
r.set(x.get() / y.get());
return r;
}
template <class R1, class R2, class R3, class R4>
quantity<typename boost::ratio_add<R1, R3>::type, typename boost::ratio_add<R2, R4>::type>
operator*(const quantity<R1, R2>& x, const quantity<R3, R4>& y)
{
typedef quantity<typename boost::ratio_add<R1, R3>::type, typename boost::ratio_add<R2, R4>::type> R;
R r;
r.set(x.get() * y.get());
return r;
}
template <class R1, class R2>
quantity<R1, R2>
operator+(const quantity<R1, R2>& x, const quantity<R1, R2>& y)
{
typedef quantity<R1, R2> R;
R r;
r.set(x.get() + y.get());
return r;
}
template <class R1, class R2>
quantity<R1, R2>
operator-(const quantity<R1, R2>& x, const quantity<R1, R2>& y)
{
typedef quantity<R1, R2> R;
R r;
r.set(x.get() - y.get());
return r;
}
// Example type-safe physics function
Distance
compute_distance(Speed v0, Time t, Acceleration a)
{
return v0 * t + Scalar(.5) * a * t * t; // if a units mistake is made here it won't compile
}
} // User1
// Exercise example type-safe physics function and show interoperation
// of custom time durations (User1::seconds) and standard time durations (std::hours).
// Though input can be arbitrary (but type-safe) units, output is always in SI-units
// (a limitation of the simplified Units lib demoed here).
int main()
{
//~ typedef boost::ratio<8, BOOST_INTMAX_C(0x7FFFFFFFD)> R1;
//~ typedef boost::ratio<3, BOOST_INTMAX_C(0x7FFFFFFFD)> R2;
typedef User1::quantity<boost::ratio_subtract<boost::ratio<0>, boost::ratio<1> >::type,
boost::ratio_subtract<boost::ratio<1>, boost::ratio<0> >::type > RR;
//~ typedef boost::ratio_subtract<R1, R2>::type RS;
//~ std::cout << RS::num << '/' << RS::den << '\n';
std::cout << "*************\n";
std::cout << "* testUser1 *\n";
std::cout << "*************\n";
User1::Distance d(( User1::mile(110) ));
boost_ex::chrono::hours h((2));
User1::Time t(( h ));
//~ boost_ex::chrono::seconds sss=boost_ex::chrono::duration_cast<boost_ex::chrono::seconds>(h);
//~ User1::seconds sss((120));
//~ User1::Time t(( sss ));
//typedef User1::quantity<boost::ratio_subtract<User1::Distance::time_dim, User1::Time::time_dim >::type,
// boost::ratio_subtract<User1::Distance::distance_dim, User1::Time::distance_dim >::type > R;
RR r=d / t;
//r.set(d.get() / t.get());
User1::Speed rc= r;
(void)rc;
User1::Speed s = d / t;
std::cout << "Speed = " << s.get() << " meters/sec\n";
User1::Acceleration a = User1::Distance( User1::foot(32.2) ) / User1::Time() / User1::Time();
std::cout << "Acceleration = " << a.get() << " meters/sec^2\n";
User1::Distance df = compute_distance(s, User1::Time( User1::seconds(0.5) ), a);
std::cout << "Distance = " << df.get() << " meters\n";
std::cout << "There are " << User1::mile::ratio::den << '/' << User1::mile::ratio::num << " miles/meter";
User1::meter mt = 1;
User1::mile mi = mt;
std::cout << " which is approximately " << mi.count() << '\n';
std::cout << "There are " << User1::mile::ratio::num << '/' << User1::mile::ratio::den << " meters/mile";
mi = 1;
mt = mi;
std::cout << " which is approximately " << mt.count() << '\n';
User1::attosecond as(1);
User1::seconds sec = as;
std::cout << "1 attosecond is " << sec.count() << " seconds\n";
std::cout << "sec = as; // compiles\n";
sec = User1::seconds(1);
as = sec;
std::cout << "1 second is " << as.count() << " attoseconds\n";
std::cout << "as = sec; // compiles\n";
std::cout << "\n";
return 0;
}