bool removed from concepts definitions as gcc-9.1 supports this syntax already

doc/DESIGN.md

@@ -580,7 +580,7 @@ a provided base class.
 namespace detail {
 
   template<typename T>
-  concept bool has_downcast = requires {
+  concept has_downcast = requires {
     downcast_guide(std::declval<downcast_base<T>>());
   };
 

src/include/units/bits/concepts.h

@@ -27,7 +27,7 @@
 namespace units {
 
   template<typename T>
-  concept bool Number = std::regular<T> &&
+  concept Number = std::regular<T> &&
       std::totally_ordered<T> &&
       requires(T a, T b) {
         { a + b } -> T;

src/include/units/bits/downcasting.h

@@ -34,7 +34,7 @@ namespace units {
   };
 
   template<typename T>
-  concept bool Downcastable =
+  concept Downcastable =
       requires {
         typename T::base_type;
       } &&
@@ -48,7 +48,7 @@ namespace units {
   namespace detail {
 
     template<typename T>
-    concept bool has_downcast = requires {
+    concept has_downcast = requires {
         downcast_guide(std::declval<downcast_base<T>>());
     };
 

src/include/units/bits/type_list.h

@@ -37,7 +37,7 @@ namespace units {
   }  // namespace detail
 
   template<typename T>
-  concept bool TypeList = detail::is_type_list<T>;
+  concept TypeList = detail::is_type_list<T>;
 
   // push_front
 

src/include/units/dimension.h

@@ -30,7 +30,7 @@
 namespace units {
 
   template<typename T>
-  concept bool BaseDimension = std::is_empty_v<T> &&
+  concept BaseDimension = std::is_empty_v<T> &&
       requires {
         { T::value } -> std::same_as<const char*>;
       };
@@ -68,7 +68,7 @@ namespace units {
   }  // namespace detail
 
   template<typename T>
-  concept bool Exponent = detail::is_exp<T>;
+  concept Exponent = detail::is_exp<T>;
 
   template<Exponent... Es>
   struct dimension;
@@ -85,7 +85,7 @@ namespace units {
   }  // namespace detail
 
   template<typename T>
-  concept bool Dimension =
+  concept Dimension =
       std::is_empty_v<T> &&
       detail::is_dimension<downcast_base_t<T>>;
 

src/include/units/dimensions/acceleration.h

@@ -29,7 +29,7 @@ namespace units {
   struct acceleration : derived_dimension<acceleration, exp<velocity, 1>, exp<base_dim_time, -1>> {};
 
   template<typename T>
-  concept bool Acceleration = QuantityOf<T, acceleration>;
+  concept Acceleration = QuantityOf<T, acceleration>;
 
   struct metre_per_second_sq : derived_unit<metre_per_second_sq, acceleration, metre, second> {};
 

src/include/units/dimensions/area.h

@@ -29,7 +29,7 @@ namespace units {
   struct area : derived_dimension<area, exp<base_dim_length, 2>> {};
 
   template<typename T>
-  concept bool Area = QuantityOf<T, area>;
+  concept Area = QuantityOf<T, area>;
 
   struct square_millimetre : derived_unit<square_millimetre, area, millimetre> {};
   struct square_centimetre : derived_unit<square_centimetre, area, centimetre> {};

src/include/units/dimensions/capacitance.h

@@ -31,7 +31,7 @@ namespace units {
   struct capacitance : derived_dimension<capacitance, exp<electric_charge, 1>, exp<voltage, -1>> {};
 
   template<typename T>
-  concept bool Capacitance =  QuantityOf<T, capacitance>;
+  concept Capacitance =  QuantityOf<T, capacitance>;
 
   struct farad : derived_unit<farad, capacitance, kilogram, metre, second, ampere> {};
 

src/include/units/dimensions/current.h

@@ -30,7 +30,7 @@ namespace units {
   struct current : derived_dimension<current, exp<base_dim_current, 1>> {};
 
   template<typename T>
-  concept bool Current = QuantityOf<T, current>;
+  concept Current = QuantityOf<T, current>;
 
   struct ampere : derived_unit<ampere, current> {};
 

src/include/units/dimensions/electric_charge.h

@@ -31,7 +31,7 @@ namespace units {
   struct electric_charge : derived_dimension<electric_charge, exp<base_dim_time, 1>, exp<base_dim_current, 1>> {};
 
   template<typename T>
-  concept bool ElectricCharge =  QuantityOf<T, electric_charge>;
+  concept ElectricCharge =  QuantityOf<T, electric_charge>;
 
   struct coulomb : derived_unit<coulomb, electric_charge, second, ampere> {};
 

src/include/units/dimensions/energy.h

@@ -31,7 +31,7 @@ namespace units {
   struct energy : derived_dimension<energy, exp<force, 1>, exp<length, 1>> {};
 
   template<typename T>
-  concept bool Energy =  QuantityOf<T, energy>;
+  concept Energy =  QuantityOf<T, energy>;
 
   struct joule : derived_unit<joule, energy, kilogram, metre, second> {};
 

src/include/units/dimensions/force.h

@@ -31,7 +31,7 @@ namespace units {
   struct force : derived_dimension<force, exp<base_dim_mass, 1>, exp<acceleration, 1>> {};
 
   template<typename T>
-  concept bool Force =  QuantityOf<T, force>;
+  concept Force =  QuantityOf<T, force>;
 
   struct newton : derived_unit<newton, force, kilogram, metre, second> {};
 

src/include/units/dimensions/frequency.h

@@ -30,7 +30,7 @@ namespace units {
   struct frequency : derived_dimension<frequency, exp<base_dim_time, -1>> {};
 
   template<typename T>
-  concept bool Frequency =  QuantityOf<T, frequency>;
+  concept Frequency =  QuantityOf<T, frequency>;
 
   struct hertz : derived_unit<hertz, frequency, second> {};
   struct millihertz : derived_unit<millihertz, milli<hertz>> {};

src/include/units/dimensions/length.h

@@ -30,7 +30,7 @@ namespace units {
   struct length : derived_dimension<length, exp<base_dim_length, 1>> {};
 
   template<typename T>
-  concept bool Length = QuantityOf<T, length>;
+  concept Length = QuantityOf<T, length>;
 
   // SI units
   struct metre : derived_unit<metre, length> {};

src/include/units/dimensions/luminous_intensity.h

@@ -30,7 +30,7 @@ namespace units {
   struct luminous_intensity : derived_dimension<luminous_intensity, exp<base_dim_luminous_intensity, 1>> {};
 
   template<typename T>
-  concept bool LuminousIntensity = QuantityOf<T, luminous_intensity>;
+  concept LuminousIntensity = QuantityOf<T, luminous_intensity>;
 
   struct candela : derived_unit<candela, luminous_intensity> {};
 

src/include/units/dimensions/mass.h

@@ -30,7 +30,7 @@ namespace units {
   struct mass : derived_dimension<mass, exp<base_dim_mass, 1>> {};
 
   template<typename T>
-  concept bool Mass = QuantityOf<T, mass>;
+  concept Mass = QuantityOf<T, mass>;
 
   struct gram : derived_unit<gram, mass, ratio<1, 1000>> {};
   struct kilogram : derived_unit<kilogram, kilo<gram>> {};

src/include/units/dimensions/power.h

@@ -30,7 +30,7 @@ namespace units {
   struct power : derived_dimension<power, exp<energy, 1>, exp<base_dim_time, -1>> {};
 
   template<typename T>
-  concept bool Power =  QuantityOf<T, power>;
+  concept Power =  QuantityOf<T, power>;
 
   struct watt : derived_unit<watt, power, kilogram, metre, second> {};
 

src/include/units/dimensions/pressure.h

@@ -31,7 +31,7 @@ namespace units {
   struct pressure : derived_dimension<pressure, exp<force, 1>, exp<area, -1>> {};
 
   template<typename T>
-  concept bool Pressure =  QuantityOf<T, pressure>;
+  concept Pressure =  QuantityOf<T, pressure>;
 
   struct pascal : derived_unit<pascal, pressure, kilogram, metre, second> {};
 

src/include/units/dimensions/substance.h

@@ -30,7 +30,7 @@ namespace units {
   struct substance : derived_dimension<substance, exp<base_dim_substance, 1>> {};
 
   template<typename T>
-  concept bool Substance = QuantityOf<T, substance>;
+  concept Substance = QuantityOf<T, substance>;
 
   struct mole : derived_unit<mole, substance> {};
 

src/include/units/dimensions/temperature.h

@@ -30,7 +30,7 @@ namespace units {
   struct temperature : derived_dimension<temperature, exp<base_dim_temperature, 1>> {};
 
   template<typename T>
-  concept bool ThermodynamicTemperature = QuantityOf<T, temperature>;
+  concept ThermodynamicTemperature = QuantityOf<T, temperature>;
 
   struct kelvin : derived_unit<kelvin, temperature> {};
 

src/include/units/dimensions/time.h

@@ -30,7 +30,7 @@ namespace units {
   struct time : derived_dimension<time, exp<base_dim_time, 1>> {};
 
   template<typename T>
-  concept bool Time = QuantityOf<T, time>;
+  concept Time = QuantityOf<T, time>;
 
   struct second : derived_unit<second, time> {};
   struct nanosecond : derived_unit<nanosecond, nano<second>> {};

src/include/units/dimensions/velocity.h

@@ -30,7 +30,7 @@ namespace units {
   struct velocity : derived_dimension<velocity, exp<base_dim_length, 1>, exp<base_dim_time, -1>> {};
 
   template<typename T>
-  concept bool Velocity = QuantityOf<T, velocity>;
+  concept Velocity = QuantityOf<T, velocity>;
 
   struct metre_per_second : derived_unit<metre_per_second, velocity, metre, second> {};
   struct kilometre_per_hour : derived_unit<kilometre_per_hour, velocity, kilometre, hour> {};

src/include/units/dimensions/voltage.h

@@ -33,7 +33,7 @@ namespace units {
   struct voltage : derived_dimension<voltage, exp<power, 1>, exp<base_dim_current, -1>> {};
 
   template<typename T>
-  concept bool Voltage =  QuantityOf<T, voltage>;
+  concept Voltage =  QuantityOf<T, voltage>;
 
   struct volt : derived_unit<volt, voltage, kilogram, metre, second, ampere> {};
 

src/include/units/dimensions/volume.h

@@ -29,7 +29,7 @@ namespace units {
   struct volume : derived_dimension<volume, exp<base_dim_length, 3>> {};
 
   template<typename T>
-  concept bool Volume = QuantityOf<T, volume>;
+  concept Volume = QuantityOf<T, volume>;
 
   struct cubic_millimetre : derived_unit<cubic_millimetre, volume, millimetre> {};
   struct cubic_centimetre : derived_unit<cubic_centimetre, volume, centimetre> {};

src/include/units/quantity.h

@@ -39,15 +39,15 @@ namespace units {
   }
 
   template<typename T>
-  concept bool Quantity = detail::is_quantity<T>;
+  concept Quantity = detail::is_quantity<T>;
 
   template<typename T, typename D>
-  concept bool QuantityOf = Quantity<T> && Dimension<D> && same_dim<typename T::dimension, D>;
+  concept QuantityOf = Quantity<T> && Dimension<D> && same_dim<typename T::dimension, D>;
 
   // Scalar
 
   template<typename T>
-  concept bool Scalar = Number<T> && !Quantity<T>;
+  concept Scalar = Number<T> && !Quantity<T>;
 
   template<Unit U, Scalar Rep>
   class quantity;

src/include/units/ratio.h

@@ -61,7 +61,7 @@ namespace units {
   }  // namespace detail
 
   template<typename T>
-  concept bool Ratio = detail::is_ratio<T>;
+  concept Ratio = detail::is_ratio<T>;
 
   // ratio_multiply
 

src/include/units/unit.h

@@ -48,7 +48,7 @@ namespace units {
   }
 
   template<typename T>
-  concept bool Unit =
+  concept Unit =
       std::is_empty_v<T> &&
       detail::is_unit<downcast_base_t<T>>;
 

test/metabench/list/type_list_concepts_all.h

@@ -56,7 +56,7 @@ namespace units {
   }  // namespace detail
 
   template<typename T>
-  concept bool TypeList = detail::is_type_list<T>;
+  concept TypeList = detail::is_type_list<T>;
 
   // push_front
 

test/metabench/list/type_list_concepts_iface.h

@@ -56,7 +56,7 @@ namespace units {
   }  // namespace detail
 
   template<typename T>
-  concept bool TypeList = detail::is_type_list<T>;
+  concept TypeList = detail::is_type_list<T>;
 
   // push_front
 

test/metabench/list/type_list_conditional_alias.h

@@ -56,7 +56,7 @@ namespace units {
   }  // namespace detail
 
   template<typename T>
-  concept bool TypeList = detail::is_type_list<T>;
+  concept TypeList = detail::is_type_list<T>;
 
   // push_front
 

test/metabench/list/type_list_conditional_alias_hard.h

@@ -49,7 +49,7 @@ namespace units {
   }  // namespace detail
 
   template<typename T>
-  concept bool TypeList = detail::is_type_list<T>;
+  concept TypeList = detail::is_type_list<T>;
 
   // push_front
 

test/metabench/list/type_list_conditional_std.h

@@ -37,7 +37,7 @@ namespace units {
   }  // namespace detail
 
   template<typename T>
-  concept bool TypeList = detail::is_type_list<T>;
+  concept TypeList = detail::is_type_list<T>;
 
   // push_front
 

test/metabench/make_dimension/dimension_concepts_all.h

@@ -79,7 +79,7 @@ namespace units {
   }  // namespace detail
 
   template<typename T>
-  concept bool Exponent = detail::is_exp<T>;
+  concept Exponent = detail::is_exp<T>;
 
   // exp_dim_id_less
 
@@ -117,7 +117,7 @@ namespace units {
   }  // namespace detail
 
   template<typename T>
-  concept bool Dimension =
+  concept Dimension =
       std::is_empty_v<T> &&
       detail::is_dimension<downcast_base_t<T>>;
 

test/metabench/make_dimension/dimension_concepts_iface.h

@@ -79,7 +79,7 @@ namespace units {
   }  // namespace detail
 
   template<typename T>
-  concept bool Exponent = detail::is_exp<T>;
+  concept Exponent = detail::is_exp<T>;
 
   // exp_dim_id_less
 
@@ -117,7 +117,7 @@ namespace units {
   }  // namespace detail
 
   template<typename T>
-  concept bool Dimension =
+  concept Dimension =
       std::is_empty_v<T> &&
       detail::is_dimension<downcast_base_t<T>>;
 

test/metabench/make_dimension/downcasting_concepts_all.h

@@ -33,7 +33,7 @@ namespace units {
   };
 
   template<typename T>
-  concept bool Downcastable =
+  concept Downcastable =
       requires {
         typename T::base_type;
       } &&

test/metabench/make_dimension/ratio_concepts_all.h

@@ -61,7 +61,7 @@ namespace units {
   }  // namespace detail
 
   template<typename T>
-  concept bool Ratio = detail::is_ratio<T>;
+  concept Ratio = detail::is_ratio<T>;
 
   // ratio_multiply
 

test/metabench/make_dimension/ratio_concepts_iface.h

@@ -61,7 +61,7 @@ namespace units {
   }  // namespace detail
 
   template<typename T>
-  concept bool Ratio = detail::is_ratio<T>;
+  concept Ratio = detail::is_ratio<T>;
 
   // ratio_multiply
 

test/metabench/make_dimension/type_list_concepts_all.h

@@ -37,7 +37,7 @@ namespace units {
   }  // namespace detail
 
   template<typename T>
-  concept bool TypeList = detail::is_type_list<T>;
+  concept TypeList = detail::is_type_list<T>;
 
   // push_front
 

test/metabench/make_dimension/type_list_concepts_iface.h

@@ -37,7 +37,7 @@ namespace units {
   }  // namespace detail
 
   template<typename T>
-  concept bool TypeList = detail::is_type_list<T>;
+  concept TypeList = detail::is_type_list<T>;
 
   // push_front
 

test/unit_test/test_custom_units.cpp

@@ -33,7 +33,7 @@ namespace {
   struct digital_information : units::derived_dimension<digital_information, units::exp<base_dim_digital_information, 1>> {};
 
   template<typename T>
-  concept bool DigitalInformation = units::QuantityOf<T, digital_information>;
+  concept DigitalInformation = units::QuantityOf<T, digital_information>;
 
   struct bit : units::derived_unit<bit, digital_information> {};
   struct byte : units::derived_unit<byte, digital_information, units::ratio<8>> {};