Replace false with impossible condition for older compiler support

Author: mborland

include/boost/decimal/decimal128_t.hpp

@@ -262,7 +262,7 @@ BOOST_DECIMAL_EXPORT class decimal128_t final
     #else
     template <typename T1, typename T2, std::enable_if_t<!detail::is_unsigned_v<T1> && detail::is_integral_v<T2>, bool> = true>
     #endif
-    constexpr decimal128_t(T1, T2, bool) noexcept { static_assert(false, "Construction from signed integer, exponent, and sign is ambiguous, so it is disallowed. You must use an Unsigned Integer for the coefficient to construct from {coefficient, exponent, sign}"); }
+    constexpr decimal128_t(T1, T2, bool) noexcept { static_assert(detail::is_unsigned_v<T1>, "Construction from signed integer, exponent, and sign is ambiguous, so it is disallowed. You must use an Unsigned Integer for the coefficient to construct from {coefficient, exponent, sign}"); }
 
     #ifdef BOOST_DECIMAL_HAS_CONCEPTS
     template <BOOST_DECIMAL_SIGNED_INTEGRAL T1, BOOST_DECIMAL_INTEGRAL T2>

include/boost/decimal/decimal32_t.hpp

@@ -287,7 +287,7 @@ BOOST_DECIMAL_EXPORT class decimal32_t final // NOLINT(cppcoreguidelines-special
     #else
     template <typename T1, typename T2, std::enable_if_t<!detail::is_unsigned_v<T1> && detail::is_integral_v<T2>, bool> = true>
     #endif
-    constexpr decimal32_t(T1, T2, bool) noexcept { static_assert(false, "Construction from signed integer, exponent, and sign is ambiguous, so it is disallowed. You must use an Unsigned Integer for the coefficient to construct from {coefficient, exponent, sign}"); }
+    constexpr decimal32_t(T1, T2, bool) noexcept { static_assert(detail::is_unsigned_v<T1>, "Construction from signed integer, exponent, and sign is ambiguous, so it is disallowed. You must use an Unsigned Integer for the coefficient to construct from {coefficient, exponent, sign}"); }
 
     #ifdef BOOST_DECIMAL_HAS_CONCEPTS
     template <BOOST_DECIMAL_SIGNED_INTEGRAL T1, BOOST_DECIMAL_INTEGRAL T2>

include/boost/decimal/decimal64_t.hpp

@@ -324,7 +324,7 @@ BOOST_DECIMAL_EXPORT class decimal64_t final
     #else
     template <typename T1, typename T2, std::enable_if_t<!detail::is_unsigned_v<T1> && detail::is_integral_v<T2>, bool> = true>
     #endif
-    constexpr decimal64_t(T1, T2, bool) noexcept { static_assert(false, "Construction from signed integer, exponent, and sign is ambiguous, so it is disallowed. You must use an Unsigned Integer for the coefficient to construct from {coefficient, exponent, sign}"); }
+    constexpr decimal64_t(T1, T2, bool) noexcept { static_assert(detail::is_unsigned_v<T1>, "Construction from signed integer, exponent, and sign is ambiguous, so it is disallowed. You must use an Unsigned Integer for the coefficient to construct from {coefficient, exponent, sign}"); }
 
     #ifdef BOOST_DECIMAL_HAS_CONCEPTS
     template <BOOST_DECIMAL_SIGNED_INTEGRAL T1, BOOST_DECIMAL_INTEGRAL T2>

include/boost/decimal/decimal_fast128_t.hpp

@@ -162,7 +162,7 @@ BOOST_DECIMAL_EXPORT class decimal_fast128_t final
     #else
     template <typename T1, typename T2, std::enable_if_t<!detail::is_unsigned_v<T1> && detail::is_integral_v<T2>, bool> = true>
     #endif
-    constexpr decimal_fast128_t(T1, T2, bool) noexcept { static_assert(false, "Construction from signed integer, exponent, and sign is ambiguous, so it is disallowed. You must use an Unsigned Integer for the coefficient to construct from {coefficient, exponent, sign}"); }
+    constexpr decimal_fast128_t(T1, T2, bool) noexcept { static_assert(detail::is_unsigned_v<T1>, "Construction from signed integer, exponent, and sign is ambiguous, so it is disallowed. You must use an Unsigned Integer for the coefficient to construct from {coefficient, exponent, sign}"); }
 
     #ifdef BOOST_DECIMAL_HAS_CONCEPTS
     template <BOOST_DECIMAL_SIGNED_INTEGRAL T1, BOOST_DECIMAL_INTEGRAL T2>

include/boost/decimal/decimal_fast32_t.hpp

@@ -151,7 +151,7 @@ BOOST_DECIMAL_EXPORT class decimal_fast32_t final
     constexpr decimal_fast32_t(T1 coeff, T2 exp, bool sign = false) noexcept;
 
     template <typename T1, typename T2, std::enable_if_t<!detail::is_unsigned_v<T1> && detail::is_integral_v<T2>, bool> = true>
-    constexpr decimal_fast32_t(T1, T2, bool) noexcept { static_assert(false, "Construction from signed integer, exponent, and sign is ambiguous, so it is disallowed. You must use an Unsigned Integer for the coefficient to construct from {coefficient, exponent, sign}"); }
+    constexpr decimal_fast32_t(T1, T2, bool) noexcept { static_assert(detail::is_unsigned_v<T1>, "Construction from signed integer, exponent, and sign is ambiguous, so it is disallowed. You must use an Unsigned Integer for the coefficient to construct from {coefficient, exponent, sign}"); }
 
     template <typename T1, typename T2, std::enable_if_t<!detail::is_unsigned_v<T1> && detail::is_integral_v<T2>, bool> = true>
     constexpr decimal_fast32_t(T1 coeff, T2 exp) noexcept;

include/boost/decimal/decimal_fast64_t.hpp

@@ -173,7 +173,7 @@ BOOST_DECIMAL_EXPORT class decimal_fast64_t final
     #else
     template <typename T1, typename T2, std::enable_if_t<!detail::is_unsigned_v<T1> && detail::is_integral_v<T2>, bool> = true>
     #endif
-    constexpr decimal_fast64_t(T1, T2, bool) noexcept { static_assert(false, "Construction from signed integer, exponent, and sign is ambiguous, so it is disallowed. You must use an Unsigned Integer for the coefficient to construct from {coefficient, exponent, sign}"); }
+    constexpr decimal_fast64_t(T1, T2, bool) noexcept { static_assert(detail::is_unsigned_v<T1>, "Construction from signed integer, exponent, and sign is ambiguous, so it is disallowed. You must use an Unsigned Integer for the coefficient to construct from {coefficient, exponent, sign}"); }
 
     #ifdef BOOST_DECIMAL_HAS_CONCEPTS
     template <BOOST_DECIMAL_SIGNED_INTEGRAL T1, BOOST_DECIMAL_INTEGRAL T2>