mp-units/test/static/natural_test.cpp

// The MIT License (MIT)
//
// Copyright (c) 2018 Mateusz Pusz
//
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#include <mp-units/systems/natural.h>

namespace {

using namespace mp_units;
using namespace mp_units::natural::unit_symbols;

// In natural units, all quantities are expressed in powers of GeV
// Quantity type safety is maintained through proper hierarchy

// Test quantity hierarchy - mass is a kind of energy
constexpr quantity test_mass = natural::mass(1. * GeV);
static_assert(QuantityOf<decltype(test_mass), natural::energy>);

// Test inverse_energy hierarchy - duration and length are both inverse_energy
constexpr quantity test_duration = natural::duration(1. / GeV);
static_assert(QuantityOf<decltype(test_duration), natural::inverse_energy>);
constexpr quantity test_length = natural::length(1. / GeV);
static_assert(QuantityOf<decltype(test_length), natural::inverse_energy>);

// Dimensional relationships still hold at the unit level
static_assert(1. / GeV / (1. / GeV) == 1. * one);                 // length/duration = speed
static_assert(1. / GeV / ((1. / GeV) * (1. / GeV)) == 1. * GeV);  // length/duration² = acceleration

// All energy-dimension quantities are compatible
static_assert(1. * GeV * (1. * one) == 1. * GeV);               // mass * velocity = momentum (dimensionally)
static_assert(1. * GeV * (1. * GeV) == 1. * GeV2);              // mass * acceleration = force
static_assert(1. * GeV * (1. * GeV) * (1. / GeV) == 1. * GeV);  // force * length = energy

// Quantity equation tests — verify that the quantity equation is convertible to (and from) the quantity
using namespace mp_units::detail;
using enum specs_convertible_result;

// speed = length / duration  (v = l/t; the l = v·t relation is derived from this equation)
static_assert(convertible(natural::speed * natural::duration, natural::length) == yes);
static_assert(convertible(natural::length, natural::speed* natural::duration) == yes);
static_assert(convertible(natural::length / natural::duration, natural::speed) == yes);

// momentum = mass * velocity  (p = mv)
static_assert(convertible(natural::mass * natural::velocity, natural::momentum) == yes);
static_assert(convertible(natural::momentum, natural::mass* natural::velocity) == yes);

// acceleration = velocity / duration  (a = dv/dt)
static_assert(convertible(natural::velocity / natural::duration, natural::acceleration) == yes);
static_assert(convertible(natural::acceleration, natural::velocity / natural::duration) == yes);

// force = mass * acceleration  (F = ma)
static_assert(convertible(natural::mass * natural::acceleration, natural::force) == yes);
static_assert(convertible(natural::force, natural::mass* natural::acceleration) == yes);

// Quantity hierarchy tests

static_assert(convertible(natural::mass, natural::energy) == yes);
static_assert(convertible(natural::energy, natural::mass) == explicit_conversion);
static_assert(convertible(natural::energy, natural::momentum) == explicit_conversion);
static_assert(convertible(natural::mass, natural::momentum) == cast);

static_assert(convertible(natural::momentum, natural::energy) == yes);
static_assert(convertible(natural::acceleration, natural::energy) == yes);
static_assert(convertible(natural::length, natural::inverse_energy) == yes);
static_assert(convertible(natural::force, natural::energy_squared) == yes);

static_assert(convertible(natural::duration, natural::inverse_energy) == yes);
static_assert(convertible(natural::inverse_energy, natural::duration) == explicit_conversion);
static_assert(convertible(natural::inverse_energy, natural::length) == explicit_conversion);
static_assert(convertible(natural::duration, natural::length) == cast);

// Dimensionless quantity tests
static_assert(convertible(natural::velocity, natural::speed) == yes);
static_assert(convertible(natural::speed, natural::velocity) == explicit_conversion);
// speed and angular_measure are separate kinds — explicit conversion needed to cross kind boundary
static_assert(convertible(natural::speed, dimensionless) == explicit_conversion_beyond_kind);
static_assert(convertible(natural::angular_measure, dimensionless) == explicit_conversion_beyond_kind);
// different dimensionless kinds cannot even be cast to each other
static_assert(convertible(natural::speed, natural::angular_measure) == no);

// Acceleration tests (acceleration has dimension energy in natural units)
static_assert(convertible(natural::acceleration, natural::energy) == yes);
static_assert(convertible(natural::energy, natural::acceleration) == explicit_conversion);

// Force tests
static_assert(convertible(natural::force, natural::energy_squared) == yes);
static_assert(convertible(natural::energy_squared, natural::force) == explicit_conversion);

// Cross-hierarchy tests (should never convert)
static_assert(convertible(natural::energy, natural::inverse_energy) == no);
static_assert(convertible(natural::energy, natural::energy_squared) == no);
static_assert(convertible(natural::energy, dimensionless) == no);

}  // namespace