🐛 fix for #512

We totally forgot to implement the comparison operators other than ==
and != for scalar types. Consequently, comparing a JSON value with a
scalar type led to compile errors.

src/json.hpp

@@ -6385,6 +6385,28 @@ class basic_json
         return operator<(lhs_type, rhs_type);
     }
 
+    /*!
+    @brief comparison: less than
+    @copydoc operator<(const_reference, const_reference)
+    */
+    template<typename ScalarType, typename std::enable_if<
+                 std::is_scalar<ScalarType>::value, int>::type = 0>
+    friend bool operator<(const_reference lhs, const ScalarType rhs) noexcept
+    {
+        return (lhs < basic_json(rhs));
+    }
+
+    /*!
+    @brief comparison: less than
+    @copydoc operator<(const_reference, const_reference)
+    */
+    template<typename ScalarType, typename std::enable_if<
+                 std::is_scalar<ScalarType>::value, int>::type = 0>
+    friend bool operator<(const ScalarType lhs, const_reference rhs) noexcept
+    {
+        return (basic_json(lhs) < rhs);
+    }
+
     /*!
     @brief comparison: less than or equal
 
@@ -6407,6 +6429,28 @@ class basic_json
         return not (rhs < lhs);
     }
 
+    /*!
+    @brief comparison: less than or equal
+    @copydoc operator<=(const_reference, const_reference)
+    */
+    template<typename ScalarType, typename std::enable_if<
+                 std::is_scalar<ScalarType>::value, int>::type = 0>
+    friend bool operator<=(const_reference lhs, const ScalarType rhs) noexcept
+    {
+        return (lhs <= basic_json(rhs));
+    }
+
+    /*!
+    @brief comparison: less than or equal
+    @copydoc operator<=(const_reference, const_reference)
+    */
+    template<typename ScalarType, typename std::enable_if<
+                 std::is_scalar<ScalarType>::value, int>::type = 0>
+    friend bool operator<=(const ScalarType lhs, const_reference rhs) noexcept
+    {
+        return (basic_json(lhs) <= rhs);
+    }
+
     /*!
     @brief comparison: greater than
 
@@ -6429,6 +6473,28 @@ class basic_json
         return not (lhs <= rhs);
     }
 
+    /*!
+    @brief comparison: greater than
+    @copydoc operator>(const_reference, const_reference)
+    */
+    template<typename ScalarType, typename std::enable_if<
+                 std::is_scalar<ScalarType>::value, int>::type = 0>
+    friend bool operator>(const_reference lhs, const ScalarType rhs) noexcept
+    {
+        return (lhs > basic_json(rhs));
+    }
+
+    /*!
+    @brief comparison: greater than
+    @copydoc operator>(const_reference, const_reference)
+    */
+    template<typename ScalarType, typename std::enable_if<
+                 std::is_scalar<ScalarType>::value, int>::type = 0>
+    friend bool operator>(const ScalarType lhs, const_reference rhs) noexcept
+    {
+        return (basic_json(lhs) > rhs);
+    }
+
     /*!
     @brief comparison: greater than or equal
 
@@ -6451,6 +6517,28 @@ class basic_json
         return not (lhs < rhs);
     }
 
+    /*!
+    @brief comparison: greater than or equal
+    @copydoc operator>=(const_reference, const_reference)
+    */
+    template<typename ScalarType, typename std::enable_if<
+                 std::is_scalar<ScalarType>::value, int>::type = 0>
+    friend bool operator>=(const_reference lhs, const ScalarType rhs) noexcept
+    {
+        return (lhs >= basic_json(rhs));
+    }
+
+    /*!
+    @brief comparison: greater than or equal
+    @copydoc operator>=(const_reference, const_reference)
+    */
+    template<typename ScalarType, typename std::enable_if<
+                 std::is_scalar<ScalarType>::value, int>::type = 0>
+    friend bool operator>=(const ScalarType lhs, const_reference rhs) noexcept
+    {
+        return (basic_json(lhs) >= rhs);
+    }
+
     /// @}
 
 

src/json.hpp.re2c

@@ -6385,6 +6385,28 @@ class basic_json
         return operator<(lhs_type, rhs_type);
     }
 
+    /*!
+    @brief comparison: less than
+    @copydoc operator<(const_reference, const_reference)
+    */
+    template<typename ScalarType, typename std::enable_if<
+                 std::is_scalar<ScalarType>::value, int>::type = 0>
+    friend bool operator<(const_reference lhs, const ScalarType rhs) noexcept
+    {
+        return (lhs < basic_json(rhs));
+    }
+
+    /*!
+    @brief comparison: less than
+    @copydoc operator<(const_reference, const_reference)
+    */
+    template<typename ScalarType, typename std::enable_if<
+                 std::is_scalar<ScalarType>::value, int>::type = 0>
+    friend bool operator<(const ScalarType lhs, const_reference rhs) noexcept
+    {
+        return (basic_json(lhs) < rhs);
+    }
+
     /*!
     @brief comparison: less than or equal
 
@@ -6407,6 +6429,28 @@ class basic_json
         return not (rhs < lhs);
     }
 
+    /*!
+    @brief comparison: less than or equal
+    @copydoc operator<=(const_reference, const_reference)
+    */
+    template<typename ScalarType, typename std::enable_if<
+                 std::is_scalar<ScalarType>::value, int>::type = 0>
+    friend bool operator<=(const_reference lhs, const ScalarType rhs) noexcept
+    {
+        return (lhs <= basic_json(rhs));
+    }
+
+    /*!
+    @brief comparison: less than or equal
+    @copydoc operator<=(const_reference, const_reference)
+    */
+    template<typename ScalarType, typename std::enable_if<
+                 std::is_scalar<ScalarType>::value, int>::type = 0>
+    friend bool operator<=(const ScalarType lhs, const_reference rhs) noexcept
+    {
+        return (basic_json(lhs) <= rhs);
+    }
+
     /*!
     @brief comparison: greater than
 
@@ -6429,6 +6473,28 @@ class basic_json
         return not (lhs <= rhs);
     }
 
+    /*!
+    @brief comparison: greater than
+    @copydoc operator>(const_reference, const_reference)
+    */
+    template<typename ScalarType, typename std::enable_if<
+                 std::is_scalar<ScalarType>::value, int>::type = 0>
+    friend bool operator>(const_reference lhs, const ScalarType rhs) noexcept
+    {
+        return (lhs > basic_json(rhs));
+    }
+
+    /*!
+    @brief comparison: greater than
+    @copydoc operator>(const_reference, const_reference)
+    */
+    template<typename ScalarType, typename std::enable_if<
+                 std::is_scalar<ScalarType>::value, int>::type = 0>
+    friend bool operator>(const ScalarType lhs, const_reference rhs) noexcept
+    {
+        return (basic_json(lhs) > rhs);
+    }
+
     /*!
     @brief comparison: greater than or equal
 
@@ -6451,6 +6517,28 @@ class basic_json
         return not (lhs < rhs);
     }
 
+    /*!
+    @brief comparison: greater than or equal
+    @copydoc operator>=(const_reference, const_reference)
+    */
+    template<typename ScalarType, typename std::enable_if<
+                 std::is_scalar<ScalarType>::value, int>::type = 0>
+    friend bool operator>=(const_reference lhs, const ScalarType rhs) noexcept
+    {
+        return (lhs >= basic_json(rhs));
+    }
+
+    /*!
+    @brief comparison: greater than or equal
+    @copydoc operator>=(const_reference, const_reference)
+    */
+    template<typename ScalarType, typename std::enable_if<
+                 std::is_scalar<ScalarType>::value, int>::type = 0>
+    friend bool operator>=(const ScalarType lhs, const_reference rhs) noexcept
+    {
+        return (basic_json(lhs) >= rhs);
+    }
+
     /// @}
 
 

test/src/unit-regression.cpp

@@ -973,4 +973,39 @@ TEST_CASE("regression tests")
         // check if serializations match
         CHECK(json::to_cbor(j2) == vec2);
     }
+
+    SECTION("issue #512 - use of overloaded operator '<=' is ambiguous")
+    {
+        json j;
+        j["a"] = 5;
+
+        // json op scalar
+        CHECK(j["a"] == 5);
+        CHECK(j["a"] != 4);
+
+        CHECK(j["a"] <= 7);
+        CHECK(j["a"] <  7);
+        CHECK(j["a"] >= 3);
+        CHECK(j["a"] >  3);
+
+
+        CHECK(not(j["a"] <= 4));
+        CHECK(not(j["a"] <  4));
+        CHECK(not(j["a"] >= 6));
+        CHECK(not(j["a"] >  6));
+
+        // scalar op json
+        CHECK(5 == j["a"]);
+        CHECK(4 != j["a"]);
+
+        CHECK(7 >= j["a"]);
+        CHECK(7 >  j["a"]);
+        CHECK(3 <= j["a"]);
+        CHECK(3 <  j["a"]);
+
+        CHECK(not(4 >= j["a"]));
+        CHECK(not(4 >  j["a"]));
+        CHECK(not(6 <= j["a"]));
+        CHECK(not(6 <  j["a"]));
+    }
 }