diff --git a/example/lambda.cpp b/example/lambda.cpp new file mode 100644 index 0000000..672c7b9 --- /dev/null +++ b/example/lambda.cpp @@ -0,0 +1,153 @@ +// Boost.Units - A C++ library for zero-overhead dimensional analysis and +// unit/quantity manipulation and conversion +// +// Copyright (C) 2003-2008 Matthias Christian Schabel +// Copyright (C) 2008 Steven Watanabe +// +// 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) + +// $Id: lambda.cpp 27 2008-06-16 14:50:58Z maehne $ + +//////////////////////////////////////////////////////////////////////// +/// +/// \file lambda.cpp +/// +/// \brief Example demonstrating the usage of Boost.Units' quantity, +/// unit, and absolute types in functors created with the +/// Boost.Lambda library and stored in Boost.Function objects. +/// +/// \author Torsten Maehne +/// \date 2008-06-04 +/// +/// A mechanical, electrical, geometrical, and thermal example +/// demonstrate how to use Boost.Units' quantity, unit, and absolute +/// types in lambda expressions. The resulting functors can be stored +/// in boost::function objects. It is also shown how to work around a +/// limitation of Boost.Lambda's bind() to help it to find the correct +/// overloaded function by specifying its signature with a +/// static_cast. +/// +//////////////////////////////////////////////////////////////////////// + +#include +#include +#include +#include +#include +#include +#include + +// Include boost/units/lambda.hpp instead of boost/lambda/lambda.hpp +// for a convenient usage of Boost.Units' quantity, unit, and absolute +// types in lambda expressions. The header augments Boost.Lambda's +// return type detuction system to recognize the new types so that not +// for each arithmetic operation the return type needs to be +// explicitely specified. +#include + +#include + + +int main(int argc, char **argv) { + + using namespace std; + namespace bl = boost::lambda; + namespace bu = boost::units; + namespace si = boost::units::si; + + + //////////////////////////////////////////////////////////////////////// + // Mechanical example: linear accelerated movement + //////////////////////////////////////////////////////////////////////// + + // Initial condition variables for acceleration, speed, and displacement + bu::quantity a = 2.0 * si::meters_per_second_squared; + bu::quantity v = 1.0 * si::meters_per_second; + bu::quantity s0 = 0.5 * si::meter; + + // Displacement over time + boost::function (bu::quantity) > + s = 0.5 * bl::var(a) * bl::_1 * bl::_1 + + bl::var(v) * bl::_1 + + bl::var(s0); + + cout << "Linear accelerated movement:" << endl + << "a = " << a << ", v = " << v << ", s0 = " << s0 << endl + << "s(1.0 * si::second) = " << s(1.0 * si::second) << endl + << endl; + + // Change initial conditions + a = 1.0 * si::meters_per_second_squared; + v = 2.0 * si::meters_per_second; + s0 = -1.5 * si::meter; + + cout << "a = " << a << ", v = " << v << ", s0 = " << s0 << endl + << "s(1.0 * si::second) = " << s(1.0 * si::second) << endl + << endl; + + + //////////////////////////////////////////////////////////////////////// + // Electrical example: oscillating current + //////////////////////////////////////////////////////////////////////// + + // Constants for the current amplitude, frequency, and offset current + const bu::quantity iamp = 1.5 * si::ampere; + const bu::quantity f = 1.0e3 * si::hertz; + const bu::quantity i0 = 0.5 * si::ampere; + + // The invocation of the sin function needs to be postponed using + // bind to specify the oscillation function. A lengthy static_cast + // to the function pointer referencing boost::units::sin() is needed + // to avoid an "unresolved overloaded function type" error. + boost::function (bu::quantity) > + i = iamp + * bl::bind(static_cast::type (*)(const bu::quantity&)>(bu::sin), + 2.0 * M_PI * si::radian * f * bl::_1) + + i0; + + cout << "Oscillating current:" << endl + << "iamp = " << iamp << ", f = " << f << ", i0 = " << i0 << endl + << "i(1.25e-3 * si::second) = " << i(1.25e-3 * si::second) << endl + << endl; + + + //////////////////////////////////////////////////////////////////////// + // Geometric example: area calculation for a square + //////////////////////////////////////////////////////////////////////// + + // Length constant + const bu::quantity l = 1.5 * si::meter; + + // Again an ugly static_cast is needed to bind pow<2> to the first + // function argument. + boost::function (bu::quantity) > + A = bl::bind(static_cast (*)(const bu::quantity&)>(bu::pow<2>), + bl::_1); + + cout << "Area of a square:" << endl + << "A(" << l <<") = " << A(l) << endl << endl; + + + //////////////////////////////////////////////////////////////////////// + // Thermal example: temperature difference of two absolute temperatures + //////////////////////////////////////////////////////////////////////// + + // Absolute temperature constants + const bu::quantity > + Tref = 273.15 * bu::absolute(); + const bu::quantity > + Tamb = 300.00 * bu::absolute(); + + boost::function (bu::quantity >, + bu::quantity >)> + dT = bl::_2 - bl::_1; + + cout << "Temperature difference of two absolute temperatures:" << endl + << "dT(" << Tref << ", " << Tamb << ") = " << dT(Tref, Tamb) << endl + << endl; + + + return 0; +}