forked from mpusz/mp-units
b982921d27
Now References can be disabled to meassure a compile time impact. Also the same examples are now provided in two subdirectories to be able to easily compare the pros and cons of every quantity construction technique.
86 lines
2.9 KiB
ReStructuredText
86 lines
2.9 KiB
ReStructuredText
Quick Start
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===========
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Here is a small example of possible operations::
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#include <units/isq/si/area.h>
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#include <units/isq/si/frequency.h>
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#include <units/isq/si/length.h>
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#include <units/isq/si/speed.h>
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#include <units/isq/si/time.h>
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using namespace units::isq::si::references;
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// simple numeric operations
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static_assert(10 * km / 2 == 5 * km);
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// unit conversions
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static_assert(1 * h == 3600 * s);
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static_assert(1 * km + 1 * m == 1001 * m);
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// dimension conversions
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inline constexpr auto kmph = km / h;
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static_assert(1 * km / (1 * s) == 1000 * (m / s));
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static_assert(2 * kmph * (2 * h) == 4 * km);
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static_assert(2 * km / (2 * kmph) == 1 * h);
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static_assert(2 * m * (3 * m) == 6 * m2);
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static_assert(10 * km / (5 * km) == 2);
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static_assert(1000 / (1 * s) == 1 * kHz);
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.. admonition:: Try it on Compiler Explorer
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`Example #1 <https://godbolt.org/z/ToTaoxKPa>`_
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This library requires some C++20 features (concepts, classes as
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:abbr:`NTTP (Non-Type Template Parameter)`, ...). Thanks to them the user gets a powerful
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but still easy to use interface where all unit conversions and dimensional analysis can be
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performed without sacrificing on accuracy. Please see the below example for a quick preview
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of basic library features::
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#include <units/format.h>
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#include <units/isq/si/length.h>
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#include <units/isq/si/speed.h>
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#include <units/isq/si/time.h>
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#include <units/isq/si/international/length.h>
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#include <units/isq/si/international/speed.h>
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#include <units/quantity_io.h>
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#include <iostream>
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using namespace units::isq;
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constexpr Speed auto avg_speed(Length auto d, Time auto t)
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{
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return d / t;
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}
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int main()
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{
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using namespace units::isq::si::literals;
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using namespace units::isq::si::references;
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constexpr Speed auto v1 = 110 * (km / h);
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constexpr Speed auto v2 = avg_speed(220_q_km, 2_q_h);
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constexpr Speed auto v3 = avg_speed(si::length<si::international::mile>(140), si::time<si::hour>(2));
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constexpr Speed auto v4 = units::quantity_cast<si::speed<si::metre_per_second>>(v2);
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constexpr Speed auto v5 = units::quantity_cast<si::metre_per_second>(v3);
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constexpr Speed auto v6 = units::quantity_cast<int>(v5);
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std::cout << v1 << '\n'; // 110 km/h
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std::cout << fmt::format("{}", v2) << '\n'; // 110 km/h
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std::cout << fmt::format("{:*^14}", v3) << '\n'; // ***70 mi/h****
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std::cout << fmt::format("{:%Q in %q}", v4) << '\n'; // 30.5556 in m/s
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std::cout << fmt::format("{0:%Q} in {0:%q}", v5) << '\n'; // 31.2928 in m/s
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std::cout << fmt::format("{:%Q}", v6) << '\n'; // 31
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}
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.. admonition:: Try it on Compiler Explorer
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`Example #2 <https://godbolt.org/z/YodshMKac>`_
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.. seealso::
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You can find more code examples in the :ref:`examples:Examples` chapter.
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