⚗ at() for std::string_view #1529

include/nlohmann/json.hpp

@@ -3492,25 +3492,25 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     written using `at()`. It also demonstrates the different exceptions that
     can be thrown.,at__object_t_key_type}
     */
-    reference at(const typename object_t::key_type& key)
+    template < class KeyType, typename std::enable_if <
+#if defined(JSON_HAS_CPP_17)
+                   std::is_same<KeyType, std::string_view>::value ||
+#endif
+                   std::is_convertible<KeyType, typename object_t::key_type>::value, int >::type    = 0 >
+    reference at(const KeyType& key)
     {
         // at only works for objects
-        if (JSON_HEDLEY_LIKELY(is_object()))
+        if (JSON_HEDLEY_UNLIKELY(is_object()))
         {
-            JSON_TRY
-            {
-                return set_parent(m_value.object->at(key));
-            }
-            JSON_CATCH (std::out_of_range&)
-            {
-                // create better exception explanation
-                JSON_THROW(out_of_range::create(403, "key '" + key + "' not found", *this));
-            }
+            JSON_THROW(type_error::create(304, "cannot use at() with " + std::string(type_name()), *this));
         }
-        else
+
+        auto it = m_value.object->find(key);
+        if (it == m_value.object->end())
         {
-            JSON_THROW(type_error::create(304, "cannot use at() with " + std::string(type_name()), *this));
+            JSON_THROW(out_of_range::create(403, "key '" + std::string(key) + "' not found", *this));
         }
+        return set_parent(it->second);
     }
 
     /*!
@@ -3543,25 +3543,25 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     `at()`. It also demonstrates the different exceptions that can be thrown.,
     at__object_t_key_type_const}
     */
-    const_reference at(const typename object_t::key_type& key) const
+    template < class KeyType, typename std::enable_if <
+#if defined(JSON_HAS_CPP_17)
+                   std::is_same<KeyType, std::string_view>::value ||
+#endif
+                   std::is_convertible<KeyType, typename object_t::key_type>::value, int >::type    = 0 >
+    const_reference at(const KeyType& key) const
     {
         // at only works for objects
-        if (JSON_HEDLEY_LIKELY(is_object()))
+        if (JSON_HEDLEY_UNLIKELY(is_object()))
         {
-            JSON_TRY
-            {
-                return m_value.object->at(key);
-            }
-            JSON_CATCH (std::out_of_range&)
-            {
-                // create better exception explanation
-                JSON_THROW(out_of_range::create(403, "key '" + key + "' not found", *this));
-            }
+            JSON_THROW(type_error::create(304, "cannot use at() with " + std::string(type_name()), *this));
         }
-        else
+
+        auto it = m_value.object->find(key);
+        if (it == m_value.object->end())
         {
-            JSON_THROW(type_error::create(304, "cannot use at() with " + std::string(type_name()), *this));
+            JSON_THROW(out_of_range::create(403, "key '" + std::string(key) + "' not found", *this));
         }
+        return it->second;
     }
 
     /*!

single_include/nlohmann/json.hpp

@@ -20305,25 +20305,25 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     written using `at()`. It also demonstrates the different exceptions that
     can be thrown.,at__object_t_key_type}
     */
-    reference at(const typename object_t::key_type& key)
+    template < class KeyType, typename std::enable_if <
+#if defined(JSON_HAS_CPP_17)
+                   std::is_same<KeyType, std::string_view>::value ||
+#endif
+                   std::is_convertible<KeyType, typename object_t::key_type>::value, int >::type    = 0 >
+    reference at(const KeyType& key)
     {
         // at only works for objects
-        if (JSON_HEDLEY_LIKELY(is_object()))
+        if (JSON_HEDLEY_UNLIKELY(is_object()))
         {
-            JSON_TRY
-            {
-                return set_parent(m_value.object->at(key));
-            }
-            JSON_CATCH (std::out_of_range&)
-            {
-                // create better exception explanation
-                JSON_THROW(out_of_range::create(403, "key '" + key + "' not found", *this));
-            }
+            JSON_THROW(type_error::create(304, "cannot use at() with " + std::string(type_name()), *this));
         }
-        else
+
+        auto it = m_value.object->find(key);
+        if (it == m_value.object->end())
         {
-            JSON_THROW(type_error::create(304, "cannot use at() with " + std::string(type_name()), *this));
+            JSON_THROW(out_of_range::create(403, "key '" + std::string(key) + "' not found", *this));
         }
+        return set_parent(it->second);
     }
 
     /*!
@@ -20356,25 +20356,25 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     `at()`. It also demonstrates the different exceptions that can be thrown.,
     at__object_t_key_type_const}
     */
-    const_reference at(const typename object_t::key_type& key) const
+    template < class KeyType, typename std::enable_if <
+#if defined(JSON_HAS_CPP_17)
+                   std::is_same<KeyType, std::string_view>::value ||
+#endif
+                   std::is_convertible<KeyType, typename object_t::key_type>::value, int >::type    = 0 >
+    const_reference at(const KeyType& key) const
     {
         // at only works for objects
-        if (JSON_HEDLEY_LIKELY(is_object()))
+        if (JSON_HEDLEY_UNLIKELY(is_object()))
         {
-            JSON_TRY
-            {
-                return m_value.object->at(key);
-            }
-            JSON_CATCH (std::out_of_range&)
-            {
-                // create better exception explanation
-                JSON_THROW(out_of_range::create(403, "key '" + key + "' not found", *this));
-            }
+            JSON_THROW(type_error::create(304, "cannot use at() with " + std::string(type_name()), *this));
         }
-        else
+
+        auto it = m_value.object->find(key);
+        if (it == m_value.object->end())
         {
-            JSON_THROW(type_error::create(304, "cannot use at() with " + std::string(type_name()), *this));
+            JSON_THROW(out_of_range::create(403, "key '" + std::string(key) + "' not found", *this));
         }
+        return it->second;
     }
 
     /*!

test/src/unit-element_access2.cpp

@@ -32,6 +32,10 @@ SOFTWARE.
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 
+#if (defined(__cplusplus) && __cplusplus >= 201703L) || (defined(_HAS_CXX17) && _HAS_CXX17 == 1)
+    #define JSON_HAS_CPP_17
+#endif
+
 TEST_CASE("element access 2")
 {
     SECTION("object")
@@ -60,6 +64,26 @@ TEST_CASE("element access 2")
                 CHECK(j_const.at("floating") == json(42.23));
                 CHECK(j_const.at("object") == json::object());
                 CHECK(j_const.at("array") == json({1, 2, 3}));
+
+#if defined(JSON_HAS_CPP_17)
+                CHECK(j.at(std::string_view("integer")) == json(1));
+                CHECK(j.at(std::string_view("unsigned")) == json(1u));
+                CHECK(j.at(std::string_view("boolean")) == json(true));
+                CHECK(j.at(std::string_view("null")) == json(nullptr));
+                CHECK(j.at(std::string_view("string")) == json("hello world"));
+                CHECK(j.at(std::string_view("floating")) == json(42.23));
+                CHECK(j.at(std::string_view("object")) == json::object());
+                CHECK(j.at(std::string_view("array")) == json({1, 2, 3}));
+
+                CHECK(j_const.at(std::string_view("integer")) == json(1));
+                CHECK(j_const.at(std::string_view("unsigned")) == json(1u));
+                CHECK(j_const.at(std::string_view("boolean")) == json(true));
+                CHECK(j_const.at(std::string_view("null")) == json(nullptr));
+                CHECK(j_const.at(std::string_view("string")) == json("hello world"));
+                CHECK(j_const.at(std::string_view("floating")) == json(42.23));
+                CHECK(j_const.at(std::string_view("object")) == json::object());
+                CHECK(j_const.at(std::string_view("array")) == json({1, 2, 3}));
+#endif
             }
 
             SECTION("access outside bounds")
@@ -1107,3 +1131,7 @@ TEST_CASE("element access 2 (throwing tests)")
     }
 }
 #endif
+
+#ifdef JSON_HAS_CPP_17
+    #undef JSON_HAS_CPP_17
+#endif