try_at_pointer and try_set_at_pointer

include/boost/json/impl/pointer.ipp

@@ -341,13 +341,23 @@ walk_pointer(
 
 } // namespace detail
 
-value const&
-value::at_pointer(string_view ptr) const&
+system::result<value const&>
+value::try_at_pointer(string_view ptr) const noexcept
 {
     system::error_code ec;
     auto const found = find_pointer(ptr, ec);
     if( !found )
-        detail::throw_system_error( ec );
+        return ec;
+    return *found;
+}
+
+system::result<value&>
+value::try_at_pointer(string_view ptr) noexcept
+{
+    system::error_code ec;
+    auto const found = find_pointer(ptr, ec);
+    if( !found )
+        return ec;
     return *found;
 }
 
@@ -484,15 +494,24 @@ value::set_at_pointer(
     return result;
 }
 
+system::result<value&>
+value::try_set_at_pointer(
+    string_view sv,
+    value_ref ref,
+    set_pointer_options const& opts )
+{
+    system::error_code ec;
+    value* result = set_at_pointer( sv, ref, ec, opts );
+    if( result )
+        return *result;
+    return ec;
+}
+
 value&
 value::set_at_pointer(
     string_view sv, value_ref ref, set_pointer_options const& opts )
 {
-    system::error_code ec;
-    value* result = set_at_pointer( sv, ref, ec, opts );
-    if( !result )
-        detail::throw_system_error( ec );
-    return *result;
+    return try_set_at_pointer(sv, ref, opts).value();
 }
 
 } // namespace json

include/boost/json/impl/value.hpp

@@ -13,17 +13,22 @@
 namespace boost {
 namespace json {
 
+value const&
+value::at_pointer(string_view ptr) const&
+{
+    return try_at_pointer(ptr).value();
+}
+
 value&
 value::at_pointer(string_view ptr) &
 {
-    auto const& self = *this;
-    return const_cast<value&>( self.at_pointer(ptr) );
+    return try_at_pointer(ptr).value();
 }
 
 value&&
 value::at_pointer(string_view ptr) &&
 {
-    return std::move( this->at_pointer(ptr) );
+    return std::move( try_at_pointer(ptr).value() );
 }
 
 } // namespace json

include/boost/json/value.hpp

@@ -3284,6 +3284,53 @@ public:
     }
     /** @} */
 
+    /** Access an element via JSON Pointer.
+
+        This function is used to access a (potentially nested) element of the
+        value using a JSON Pointer string.
+
+        @par Complexity
+        Linear in the sizes of `ptr` and underlying array, object, or string.
+
+        @par Exception Safety
+        No-throw guarantee.
+
+        @param ptr JSON Pointer string.
+
+        @return `boost::system::result<value&>` containing either a reference
+            to the element identified by `ptr` or a corresponding `error_code`.
+
+        @see
+            [RFC 6901 - JavaScript Object Notation (JSON) Pointer](https://datatracker.ietf.org/doc/html/rfc6901).
+    */
+    BOOST_JSON_DECL
+    system::result<value const&>
+    try_at_pointer(string_view ptr) const noexcept;
+
+    /** Access an element via JSON Pointer.
+
+        This function is used to access a (potentially nested) element of the
+        value using a JSON Pointer string.
+
+        @par Complexity
+        Linear in the sizes of `ptr` and underlying array, object, or string.
+
+        @par Exception Safety
+        No-throw guarantee.
+
+        @param ptr JSON Pointer string.
+
+        @return `boost::system::result<value const&>` containing either a
+            reference to the element identified by `ptr` or a corresponding
+            `error_code`.
+
+        @see
+            [RFC 6901 - JavaScript Object Notation (JSON) Pointer](https://datatracker.ietf.org/doc/html/rfc6901).
+    */
+    BOOST_JSON_DECL
+    system::result<value&>
+    try_at_pointer(string_view ptr) noexcept;
+
     /** Access an element via JSON Pointer.
 
         This function is used to access a (potentially nested)
@@ -3306,7 +3353,7 @@ public:
             RFC 6901 - JavaScript Object Notation (JSON) Pointer</a>
     */
     /** @{ */
-    BOOST_JSON_DECL
+    inline
     value const&
     at_pointer(string_view ptr) const&;
 
@@ -3360,6 +3407,72 @@ public:
 
     //------------------------------------------------------
 
+    /** Set an element via JSON Pointer.
+
+        This function is used to insert or assign to a potentially nested
+        element of the value using a JSON Pointer string. The function may
+        create intermediate elements corresponding to pointer segments.
+        <br/>
+
+        The particular conditions when and what kind of intermediate element
+        is created is governed by the `ptr` parameter.
+
+        Each pointer token is considered in sequence. For each token
+
+        - if the containing value is an @ref object, then a new `null`
+          element is created with key equal to unescaped token string;
+          otherwise
+
+        - if the containing value is an @ref array, and the token represents a
+          past-the-end marker, then a `null` element is appended to the array;
+          otherwise
+
+        - if the containing value is an @ref array, and the token represents a
+          number, then if the difference between the number and array's size
+          is smaller than `opts.max_created_elements`, then the size of the
+          array is increased, so that the number can reference an element in the
+          array; otherwise
+
+        - if the containing value is of different @ref kind and
+          `opts.replace_any_scalar` is `true`, or the value is `null`, then
+
+           - if `opts.create_arrays` is `true` and the token either represents
+             past-the-end marker or a number, then the value is replaced with
+             an empty array and the token is considered again; otherwise
+
+           - if `opts.create_objects` is `true`, then the value is replaced
+             with an empty object and the token is considered again; otherwise
+
+        - an error is produced.
+
+        @par Complexity
+        Linear in the sum of size of `ptr`, size of underlying array, object,
+        or string and `opts.max_created_elements`.
+
+        @par Exception Safety
+        Basic guarantee.
+        Calls to `memory_resource::allocate` may throw.
+
+        @param sv JSON Pointer string.
+
+        @param ref The value to assign to pointed element.
+
+        @param opts The options for the algorithm.
+
+        @return `boost::json::result<value&>` containing either a reference to
+            the element identified by `ptr` or a corresponding `error_code`.
+
+        @see
+            @ref set_pointer_options,
+            [RFC 6901 - JavaScript Object Notation (JSON) Pointer](https://datatracker.ietf.org/doc/html/rfc6901).
+    */
+    BOOST_JSON_DECL
+    system::result<value&>
+    try_set_at_pointer(
+        string_view sv,
+        value_ref ref,
+        set_pointer_options const& opts = {} );
+
     /** Set an element via JSON Pointer.
 
         This function is used to insert or assign to a potentially nested

test/pointer.cpp

@@ -346,6 +346,22 @@ public:
         BOOST_TEST( hasLocation(ec) );
     }
 
+    void
+    testTry()
+    {
+        value jv = testValue();
+        BOOST_TEST( &jv.try_at_pointer("/foo").value() == &jv.at("foo") );
+        BOOST_TEST_THROWS_WITH_LOCATION( jv.try_at_pointer("foo").value() );
+
+        value const& cjv = jv;
+        BOOST_TEST( &cjv.try_at_pointer("/foo").value() == &cjv.at("foo") );
+        BOOST_TEST_THROWS_WITH_LOCATION( cjv.try_at_pointer("foo").value() );
+
+        auto result = jv.try_set_at_pointer("", array());
+        BOOST_TEST(( jv == array() ));
+        BOOST_TEST( &*result == &jv );
+    }
+
     void
     run()
     {
@@ -359,6 +375,7 @@ public:
         testSet();
         testSetNonThrowing<system::error_code>();
         testSetNonThrowing<std::error_code>();
+        testTry();
     }
 };