JSON as_or accessor

doc/ref/corelib/basic_json.md

@@ -206,6 +206,10 @@ for their storage, otherwise attempts to return a default constructed allocator.
     <td><a href="json/at.md">at<br>at_or_null</a></td>
     <td>Return the specified value.</td> 
   </tr>
+  <tr>
+    <td><a href="json/as_or.md">at<br>at_or_null</a></td>
+    <td>Attempts to convert a basic_json value to a value of a type if it matches, otherwise a default value.</td> 
+  </tr>
   <tr>
     <td><a href="json/get_value_or.md">get_value_or</a></td>
     <td>Return the specified value if available, otherwise a default value.</td> 

doc/ref/corelib/json/as.md

@@ -55,7 +55,7 @@ Output:
 (1) 2147483647
 (2) -2147483648
 (3) 2147483648
-(4) ÷
+(4) �
 (5) 4294967286
 (6) 10
 (7) 10.5

doc/ref/corelib/json/as_or.md

@@ -0,0 +1,55 @@
+### jsoncons::basic_json::as_or
+
+```cpp
+template <typename T,typename U>
+T as_or(U&& default_value) const; 
+```
+
+Checks the value of the json value with the template value using [json_type_traits](../json_type_traits.md), and converts if it matches, or returns a default value if it doesn't.
+
+See [as](as.md) for details on the value returned.
+
+### Type requirements
+
+- `U` must be convertible to `T`
+
+### Examples
+
+#### Return a value if the type matches, or a default value otherwise
+
+```cpp
+#include <jsoncons/json.hpp>
+
+int main()
+{
+    json j = json::parse("\"Hello World\"");
+
+    std::cout << j.as_or<int>(-1) << "\n";
+    std::cout << j.as_or<std::string>("null") << "\n";
+}
+```
+Output:
+```
+-1
+Hello World
+```
+
+#### Return a value if it exists and the type matches, or a default value otherwise
+
+```cpp
+#include <jsoncons/json.hpp>
+
+int main()
+{
+    json j(json_object_arg, {{"author","Evelyn Waugh"},{"title","Sword of Honour"},{"id","0"}});
+    std::cout << j.at_or_null("author").as_or<std::string>("unknown") << "\n";
+    std::cout << j.at_or_null("category").as_or<std::string>("fiction") << "\n";
+    std::cout << j.at_or_null("id").as_or<int>(-1) << "\n";
+}
+```
+Output:
+```
+Evelyn Waugh
+fiction
+-1
+```

doc/ref/corelib/json/get_value_or.md

@@ -1,7 +1,7 @@
 ### jsoncons::basic_json::get_value_or
 
 ```cpp
-template <typename T,class U>
+template <typename T,typename U>
 T get_value_or(const string_view_type& name, U&& default_value) const; 
 ```
 

include/jsoncons/basic_json.hpp

@@ -3699,6 +3699,24 @@ namespace jsoncons {
             }
         }
 
+        template <typename T,typename U>
+        typename std::enable_if<is_json_type_traits_specialized<basic_json,T>::value,T>::type
+        as_or(U&& default_value) const
+        {
+            static_assert(std::is_convertible<U&&, T>::value,
+                          "as_or: U must be convertible to T");
+            using T_type_traits = json_type_traits<basic_json,T>;
+            if (T_type_traits::is(*this))
+            {
+                T val = T_type_traits::as(*this);
+                return val;
+            }
+            else
+            {
+                return static_cast<T>(std::forward<U>(default_value));
+            }
+        }
+
         const basic_json& at_or_null(const string_view_type& key) const
         {
             switch (storage_kind())

test/corelib/src/json_object_tests.cpp

@@ -297,6 +297,40 @@ TEST_CASE("test_empty_object_move_assignment")
     CHECK(c.is_object());
 }
 
+TEST_CASE("as_or test")
+{
+    json a = json::parse(R"(
+    {
+        "key1" : "value1",
+        "key2" : "3.7",
+        "key3" : 1.5,
+        "key4" : 1
+    }
+    )");
+
+    std::string s1 = a.as_or<std::string>("null");
+    std::string s2 = a["key1"].as_or<std::string>("null");
+    std::string s3 = a["key2"].as_or<std::string>("null");
+    std::string s4 = a["key3"].as_or<std::string>("null");
+    int i1 = a["key1"].as_or<int>(-1);
+    int i2 = a["key3"].as_or<int>(-1);
+    int i3 = a["key4"].as_or<int>(-1);
+    double d1 = a["key2"].as_or<double>(-1.0);
+    double d2 = a["key3"].as_or<double>(-1.0);
+    double d3 = a["key4"].as_or<double>(-1.0);
+
+    CHECK(s1 == std::string("null"));
+    CHECK(s2 == std::string("value1"));
+    CHECK(s3 == std::string("3.7"));
+    CHECK(s4 == std::string("null"));
+    CHECK(i1 == -1);
+    CHECK(i2 == -1);
+    CHECK(i3 == 1);
+    CHECK(d1 == -1.0);
+    CHECK(d2 == 1.5);
+    CHECK(d3 == -1.0);
+}
+
 TEST_CASE("at_or_null test")
 {
     json a = json::parse(R"(