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Use User-defined literals #2235

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00947be
use udl
esseivaju Feb 5, 2026
a011bf6
always return double
esseivaju Feb 6, 2026
92fe6aa
fix deprecated syntax
esseivaju Feb 6, 2026
6c7e9a7
long double
esseivaju Feb 6, 2026
d8beeb2
using namespace
esseivaju Feb 6, 2026
3aff456
revert long double
esseivaju Feb 6, 2026
3aefebf
doc
esseivaju Feb 6, 2026
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41 changes: 20 additions & 21 deletions src/celeritas/Units.hh
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Expand Up @@ -178,34 +178,33 @@ CELER_ICC barn = Constant{1e-24} * centimeter * centimeter;
* \endcode
*
* \note In headers, prefer explicit multiplication (e.g., \c 2.5 *
* units::centimeter) or bring in only the needed literal operator inside a
* function scope:
* units::centimeter) or bring the namespace inside a function scope:
* \code
* using celeritas::units::literals::operator"" _centimeter;
* using namespace celeritas::units::literals;
* return 2.5_centimeter;
* \endcode
*/
namespace literals
{

#define CELER_DEFINE_UNIT_UDL(SUFFIX, NAME) \
CELER_CONSTEXPR_FUNCTION real_type operator""_##SUFFIX(long double v) \
{ \
return static_cast<real_type>(v) * units::NAME; \
} \
CELER_CONSTEXPR_FUNCTION Constant operator""_##SUFFIX( \
unsigned long long int v) \
{ \
return v * units::NAME; \
} \
CELER_CONSTEXPR_FUNCTION real_type operator""_##NAME(long double v) \
{ \
return static_cast<real_type>(v) * units::NAME; \
} \
CELER_CONSTEXPR_FUNCTION Constant operator""_##NAME( \
unsigned long long int v) \
{ \
return v * units::NAME; \
#define CELER_DEFINE_UNIT_UDL(SUFFIX, NAME) \
CELER_CONSTEXPR_FUNCTION double operator""_##SUFFIX(long double v) \
{ \
return v * units::NAME; \
} \
CELER_CONSTEXPR_FUNCTION Constant operator""_##SUFFIX( \
unsigned long long int v) \
{ \
return v * units::NAME; \
} \
CELER_CONSTEXPR_FUNCTION double operator""_##NAME(long double v) \
{ \
return v * units::NAME; \
} \
CELER_CONSTEXPR_FUNCTION Constant operator""_##NAME( \
unsigned long long int v) \
{ \
return v * units::NAME; \
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@sethrj sethrj Feb 6, 2026

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Copilot's gone crazy

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@esseivaju esseivaju Feb 6, 2026 •
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We have to return double (or long double if we care about it?) which matches the Constant interface returning the literal type, and not real_type

}

CELER_DEFINE_UNIT_UDL(cm, centimeter)
Expand Down
4 changes: 2 additions & 2 deletions src/celeritas/em/distribution/WentzelDistribution.hh
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Expand Up @@ -271,8 +271,8 @@ CELER_FUNCTION real_type WentzelDistribution::flat_form_factor(real_type x)
*/
CELER_CONSTEXPR_FUNCTION real_type WentzelDistribution::flat_coeff()
{
return native_value_to<units::MevMomentum>(2 * units::femtometer
/ constants::hbar_planck)
using namespace celeritas::units::literals;
return native_value_to<units::MevMomentum>(2.0_fm / constants::hbar_planck)
.value();
}

Expand Down
3 changes: 2 additions & 1 deletion src/celeritas/em/msc/detail/UrbanMscSafetyStepLimit.hh
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Expand Up @@ -81,7 +81,8 @@ class UrbanMscSafetyStepLimit
//! Minimum range for an empirical step-function approach
static CELER_CONSTEXPR_FUNCTION real_type min_range()
{
return 1e-3 * units::centimeter;
using namespace celeritas::units::literals;
return 1e-3_cm;
}

//! Maximum step over the range
Expand Down
3 changes: 2 additions & 1 deletion src/celeritas/em/msc/detail/UrbanMscScatter.hh
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Expand Up @@ -105,7 +105,8 @@ class UrbanMscScatter
//! The minimum step length for geometry 0.05 nm
static CELER_CONSTEXPR_FUNCTION real_type geom_min()
{
return 5e-9 * units::centimeter;
using namespace celeritas::units::literals;
return 5e-9_cm;
}

//// HELPER FUNCTIONS ////
Expand Down
9 changes: 7 additions & 2 deletions src/celeritas/ext/detail/NaviTouchableUpdater.hh
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Expand Up @@ -39,12 +39,17 @@ class NaviTouchableUpdater final : public TouchableUpdaterInterface

public:
//! Maximum step to try within the current volume [len]
static constexpr double max_step() { return 1.0 * units::millimeter; }
static constexpr double max_step()
{
using namespace celeritas::units::literals;
return 1.0_mm;
}

//! Print diagnostic when the step is greater than this amount [len]
static constexpr double max_quiet_step()
{
return 1e-3 * units::millimeter;
using namespace celeritas::units::literals;
return 1e-3_mm;
}

// Construct from detector LVs
Expand Down
6 changes: 4 additions & 2 deletions src/celeritas/phys/PhysicsOptions.hh
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Expand Up @@ -64,7 +64,8 @@ struct ParticleOptions
static ParticleOptions default_light()
{
ParticleOptions opts;
opts.min_range = real_type{1} * units::millimeter;
using namespace celeritas::units::literals;
opts.min_range = 1.0_mm;
opts.max_step_over_range = 0.2;
opts.lowest_energy = ParticleOptions::Energy{0.001};
opts.displaced = true;
Expand All @@ -77,7 +78,8 @@ struct ParticleOptions
static ParticleOptions default_heavy()
{
ParticleOptions opts;
opts.min_range = 0.1 * units::millimeter;
using namespace celeritas::units::literals;
opts.min_range = 0.1_mm;
opts.max_step_over_range = 0.2;
opts.lowest_energy = ParticleOptions::Energy{0.001};
opts.displaced = false;
Expand Down
12 changes: 6 additions & 6 deletions test/celeritas/Constants.test.cc
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Expand Up @@ -27,6 +27,7 @@ namespace constants
{
namespace test
{
using namespace celeritas::units::literals;
//---------------------------------------------------------------------------//
// CLHEP units introduce extra error due to repeated operations with
// non-representable values
Expand Down Expand Up @@ -73,7 +74,7 @@ TEST(ConstantsTest, clhep_codata)
// Values differ from the CLHEP constants (CODATA 2006) by ~1e-7 due to
// the 2019 change in SI using e- charge as an exact definition
// rather than a measured constant
constexpr Constant old_e_electron{1.602176487e-19 * units::coulomb};
constexpr Constant old_e_electron{1.602176487e-19_C};

using MevMass = Quantity<units::MevPerCsq, double>;

Expand Down Expand Up @@ -123,13 +124,12 @@ TEST(ConstantsTest, clhep)
TEST(ConstantsTest, derivative)
{
// Compared against definition of Dalton, table 8 of SI 2019
EXPECT_SOFT_EQ(1.66053906660e-27 * units::kilogram, atomic_mass);
EXPECT_SOFT_EQ(1.602176634e-19 * units::joule, e_electron * units::volt);
EXPECT_SOFT_EQ(1.66053906660e-27_kg, atomic_mass);
EXPECT_SOFT_EQ(1.602176634e-19_J, e_electron * units::volt);

// CODATA 2018 listings
EXPECT_SOFT_NEAR(1.49241808560e-10 * units::joule,
atomic_mass * c_light * c_light,
clhep_tol);
EXPECT_SOFT_NEAR(
1.49241808560e-10_J, atomic_mass * c_light * c_light, clhep_tol);
EXPECT_SOFT_NEAR(931.49410242e6 * e_electron * units::volt,
atomic_mass * c_light * c_light,
clhep_tol);
Expand Down
9 changes: 4 additions & 5 deletions test/celeritas/Units.test.cc
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Expand Up @@ -24,6 +24,7 @@ namespace units
{
namespace test
{
using namespace celeritas::units::literals;
//---------------------------------------------------------------------------//
// Locally replace the Celeritas "real" expectation for one that forces
// Constant objects to double-precision
Expand Down Expand Up @@ -97,8 +98,6 @@ TEST(UnitsTest, trait_visitor)
//---------------------------------------------------------------------------//
TEST(UnitsTest, literals)
{
using namespace celeritas::units::literals;

EXPECT_REAL_EQ(2.5 * units::centimeter, 2.5_centimeter);
EXPECT_REAL_EQ(2.5 * units::centimeter, 2.5_cm);
EXPECT_REAL_EQ(3 * units::meter, 3_meter);
Expand Down Expand Up @@ -158,20 +157,20 @@ TEST(UnitsTest, clhep)

double g4_native = 2.5 * CLHEP::tesla;
auto celer_native = convert_from_geant(g4_native, clhep_field);
EXPECT_SOFT_EQ(2.5 * units::tesla, celer_native);
EXPECT_SOFT_EQ(2.5_T, celer_native);
EXPECT_SOFT_EQ(2.5, native_value_to<FieldTesla>(celer_native).value());
EXPECT_SOFT_EQ(g4_native, convert_to_geant(celer_native, clhep_field));
}
{
double g4_native = 1.5 * CLHEP::s;
auto celer_native = convert_from_geant(g4_native, clhep_time);
EXPECT_SOFT_EQ(1.5 * units::second, celer_native);
EXPECT_SOFT_EQ(1.5_s, celer_native);
EXPECT_SOFT_EQ(g4_native, convert_to_geant(celer_native, clhep_time));
}
{
double g4_native = 1.5 * CLHEP::meter;
auto celer_native = convert_from_geant(g4_native, clhep_length);
EXPECT_SOFT_EQ(1.5 * units::meter, celer_native);
EXPECT_SOFT_EQ(1.5_m, celer_native);
EXPECT_SOFT_EQ(g4_native, convert_to_geant(celer_native, clhep_length));
}
#else
Expand Down
9 changes: 5 additions & 4 deletions test/celeritas/em/distribution/EnergyLossHelper.test.cc
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Expand Up @@ -26,6 +26,7 @@ namespace celeritas
{
namespace test
{
using namespace celeritas::units::literals;
//---------------------------------------------------------------------------//
using units::MevEnergy;
using EnergySq = RealQuantity<UnitProduct<units::Mev, units::Mev>>;
Expand Down Expand Up @@ -156,7 +157,7 @@ TEST_F(EnergyLossDistributionTest, none)
MevEnergy mean_loss{2e-6};

// Tiny step, little energy loss
real_type step = 1e-6 * units::centimeter;
real_type step = 1e-6_cm;
EnergyLossHelper helper(
fluct->host_ref(), cutoff, material, particle, mean_loss, step);
EXPECT_EQ(EnergyLossFluctuationModel::none, helper.model());
Expand All @@ -180,7 +181,7 @@ TEST_F(EnergyLossDistributionTest, gaussian)

// Larger step samples from gamma distribution, smaller step from Gaussian
{
real_type step = 5e-2 * units::centimeter;
real_type step = 5e-2_cm;
EnergyLossHelper helper(
fluct->host_ref(), cutoff, material, particle, mean_loss, step);
EXPECT_EQ(EnergyLossFluctuationModel::gamma, helper.model());
Expand All @@ -203,7 +204,7 @@ TEST_F(EnergyLossDistributionTest, gaussian)
EXPECT_REF_EQ(ref, sampled);
}
{
real_type step = 5e-4 * units::centimeter;
real_type step = 5e-4_cm;
EnergyLossHelper helper(
fluct->host_ref(), cutoff, material, particle, mean_loss, step);
EXPECT_SOFT_EQ(0.00019160444039613,
Expand Down Expand Up @@ -251,7 +252,7 @@ TEST_F(EnergyLossDistributionTest, urban)
material = {PhysMatId{0}};
CutoffView cutoff(cutoffs->host_ref(), PhysMatId{0});
MevEnergy mean_loss{0.01};
real_type step = 0.01 * units::centimeter;
real_type step = 0.01_cm;

EnergyLossHelper helper(
fluct->host_ref(), cutoff, material, particle, mean_loss, step);
Expand Down
16 changes: 8 additions & 8 deletions test/celeritas/field/FieldPropagator.test.cc
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Expand Up @@ -40,6 +40,7 @@ namespace celeritas
{
namespace test
{
using namespace celeritas::units::literals;
//---------------------------------------------------------------------------//
constexpr real_type pi{constants::pi};
constexpr real_type sqrt_three{constants::sqrt_three};
Expand Down Expand Up @@ -156,8 +157,7 @@ struct HorribleZField

// Field value (native units) for 10 MeV electron/positron to have a radius of
// 1 cm
constexpr real_type unit_radius_field_strength{3.5019461121752274
* units::tesla};
constexpr real_type unit_radius_field_strength{3.5019461121752274_T};

//---------------------------------------------------------------------------//
// TESTS
Expand All @@ -171,7 +171,7 @@ TEST_F(TwoBoxesTest, electron_interior)
auto particle
= this->make_particle_view(pdg::electron(), MevEnergy{10.9181415106});
auto geo = this->make_geo_track_view({radius, 0, 0}, {0, 1, 0});
UniformZField field(1.0 * units::tesla);
UniformZField field(1.0_T);

// Check expected field curvature and geometry cell
EXPECT_SOFT_EQ(radius, this->calc_field_curvature(particle, geo, field));
Expand Down Expand Up @@ -348,7 +348,7 @@ TEST_F(TwoBoxesTest, gamma_pathological)
auto particle = this->make_particle_view(pdg::gamma(), MevEnergy{1});

// Construct field (shape and magnitude shouldn't matter)
HorribleZField field{1.2345 * units::tesla, 5};
HorribleZField field{1.2345_T, 5};
FieldDriverOptions driver_options;
auto integrate = make_mag_field_integrator<DiagnosticDPIntegrator>(
field, particle.charge());
Expand Down Expand Up @@ -446,7 +446,7 @@ TEST_F(TwoBoxesTest, gamma_exit)
TEST_F(TwoBoxesTest, electron_super_small_step)
{
auto particle = this->make_particle_view(pdg::electron(), MevEnergy{2});
UniformZField field(static_cast<real_type>(1 * units::tesla));
UniformZField field(static_cast<real_type>(1_T));
FieldDriverOptions driver_options;

std::vector<real_type> intersect_distance;
Expand Down Expand Up @@ -1144,7 +1144,7 @@ TEST_F(LayersTest, revolutions_through_layers)
auto particle
= this->make_particle_view(pdg::electron(), MevEnergy{10.9181415106});
auto geo = this->make_geo_track_view({radius, 0, 0}, {0, 1, 0});
UniformZField field(1.0 * units::tesla);
UniformZField field(1.0_T);

// Build propagator
FieldDriverOptions driver_options;
Expand Down Expand Up @@ -1231,7 +1231,7 @@ TEST_F(SimpleCmsTest, TEST_IF_CELERITAS_DOUBLE(electron_stuck))
{
auto particle = this->make_particle_view(pdg::electron(),
MevEnergy{4.25402379798713e-01});
UniformZField field(real_type(1 * units::tesla));
UniformZField field(real_type(1_T));
FieldDriverOptions driver_options;

auto geo = this->make_geo_track_view(
Expand Down Expand Up @@ -1329,7 +1329,7 @@ TEST_F(SimpleCmsTest, TEST_IF_CELERITAS_DOUBLE(electron_stuck))

TEST_F(SimpleCmsTest, TEST_IF_CELERITAS_DOUBLE(vecgeom_failure))
{
UniformZField field(real_type(1 * units::tesla));
UniformZField field(real_type(1_T));
FieldDriverOptions driver_options;
driver_options.max_substeps = 100;

Expand Down
19 changes: 10 additions & 9 deletions test/celeritas/field/FieldSubstepper.test.cc
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Expand Up @@ -31,6 +31,7 @@ namespace celeritas
{
namespace test
{
using namespace celeritas::units::literals;

constexpr real_type sqrt_two{constants::sqrt_two};
using units::ElementaryCharge;
Expand Down Expand Up @@ -87,8 +88,8 @@ class RevolutionFieldSubstepperTest : public FieldSubstepperTest
// Input parameters of an electron in a uniform magnetic field
test_params.nsteps = 100;
test_params.revolutions = 10;
test_params.radius = 3.8085386036 * units::centimeter;
test_params.delta_z = 6.7003310629 * units::centimeter;
test_params.radius = 3.8085386036_cm;
test_params.delta_z = 6.7003310629_cm;
test_params.epsilon = 1.0e-5;
}

Expand Down Expand Up @@ -117,7 +118,7 @@ make_mag_field_substepper(FieldT&& field,
//! Z oriented field of 2**(y / scale)
struct ExpZField
{
real_type strength{1 * units::tesla};
real_type strength{1_T};
real_type scale{1};

Real3 operator()(Real3 const& pos) const
Expand Down Expand Up @@ -168,7 +169,7 @@ TEST_F(FieldSubstepperTest, unpleasant_field)
FieldDriverOptions driver_options;
driver_options.max_nsteps = 32;

real_type field_strength = 1.0 * units::tesla;
real_type field_strength = 1.0_T;
MevEnergy e{1.0};
real_type radius = this->calc_curvature(e, field_strength);

Expand Down Expand Up @@ -200,7 +201,7 @@ TEST_F(FieldSubstepperTest, horrible_field)
FieldDriverOptions driver_options;
driver_options.max_nsteps = 32;

real_type field_strength = 1.0 * units::tesla;
real_type field_strength = 1.0_T;
MevEnergy e{1.0};
real_type radius = this->calc_curvature(e, field_strength);

Expand Down Expand Up @@ -240,7 +241,7 @@ TEST_F(FieldSubstepperTest, pathological_chord)
FieldDriverOptions driver_options;
driver_options.max_nsteps = std::numeric_limits<short int>::max();

real_type field_strength = 1.0 * units::tesla;
real_type field_strength = 1.0_T;
MevEnergy e{1.0};
real_type radius = this->calc_curvature(e, field_strength);

Expand Down Expand Up @@ -279,7 +280,7 @@ TEST_F(FieldSubstepperTest, step_counts)
FieldDriverOptions driver_options;
driver_options.max_nsteps = std::numeric_limits<short int>::max();

real_type field_strength = 1.0 * units::tesla;
real_type field_strength = 1.0_T;
auto integrate = make_mag_field_integrator<DiagnosticDPIntegrator>(
UniformZField{field_strength}, units::ElementaryCharge{-1});

Expand Down Expand Up @@ -340,7 +341,7 @@ TEST_F(FieldSubstepperTest, step_counts)
TEST_F(RevolutionFieldSubstepperTest, advance)
{
auto advance = make_mag_field_substepper<DormandPrinceIntegrator>(
UniformZField{1.0 * units::tesla}, driver_options, electron_charge());
UniformZField{1.0_T}, driver_options, electron_charge());

// Test parameters and the sub-step size
real_type circumference = 2 * constants::pi * test_params.radius;
Expand Down Expand Up @@ -382,7 +383,7 @@ TEST_F(RevolutionFieldSubstepperTest, advance)
TEST_F(RevolutionFieldSubstepperTest, accurate_advance)
{
auto advance = make_mag_field_substepper<DormandPrinceIntegrator>(
UniformZField{1.0 * units::tesla}, driver_options, electron_charge());
UniformZField{1.0_T}, driver_options, electron_charge());

// Test parameters and the sub-step size
real_type circumference = 2 * constants::pi * test_params.radius;
Expand Down
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