Add cpp:custom-print for classes

cpp/include/Ice/Value.h

@@ -71,11 +71,10 @@ namespace Ice
          */
         [[nodiscard]] SlicedDataPtr ice_getSlicedData() const;
 
-        /**
-         * Outputs a description of this instance to the stream. This description includes the type name and the name
-         * and value of all the fields of this instance.
-         * @param os The output stream.
-         */
+        /// Outputs a description of this instance to the stream. This description includes the type name and the name
+        /// and value of all the fields of this instance.
+        /// Use ["cpp:custom-print"] to tell the Slice compiler to generate an override implemented by the application.
+        /// @param os The output stream.
         virtual void ice_print(std::ostream& os) const;
 
         /// Outputs the name and value of each field of this instance, including inherited fields, to the stream.
@@ -111,8 +110,17 @@ namespace Ice
         SlicedDataPtr _slicedData;
     };
 
-    /// Outputs the description of a class instance to the stream by calling the ice_print member function when this
-    /// instance is not null.
+    /// Outputs the description of a class instance to the stream. This function calls ice_print on value.
+    /// @param os The output stream.
+    /// @param value The class instance.
+    /// @return The output stream.
+    inline std::ostream& operator<<(std::ostream& os, const Value& value)
+    {
+        value.ice_print(os);
+        return os;
+    }
+
+    /// Outputs the description of a class instance held in a shared_ptr.
     /// @tparam T The class type.
     /// @param os The output stream.
     /// @param value The class instance held in a shared pointer. May be null.
@@ -122,7 +130,7 @@ namespace Ice
     {
         if (value)
         {
-            value->ice_print(os);
+            os << *value;
         }
         else
         {

cpp/src/slice2cpp/Gen.cpp

@@ -878,7 +878,7 @@ Slice::Gen::validateMetadata(const UnitPtr& u)
 
     // "cpp:custom-print"
     MetadataInfo customPrintInfo = {
-        .validOn = {typeid(Struct)},
+        .validOn = {typeid(Struct), typeid(ClassDecl)},
         .acceptedArgumentKind = MetadataArgumentKind::NoArguments,
     };
     knownMetadata.emplace("cpp:custom-print", std::move(customPrintInfo));
@@ -2334,6 +2334,13 @@ Slice::Gen::DataDefVisitor::visitClassDefEnd(const ClassDefPtr& p)
         emitDataMember(dataMember);
     }
 
+    if (p->hasMetadata("cpp:custom-print"))
+    {
+        H << sp;
+        H << nl << "// Custom ice_print implemented by the application.";
+        H << nl << "void ice_print(std::ostream& os) const override;";
+    }
+
     const string baseClass = base ? getUnqualified(base->mappedScoped(), scope) : getUnqualified("::Ice::Value", scope);
 
     if (!dataMembers.empty())

cpp/test/Ice/print/AllTests.cpp

@@ -9,6 +9,17 @@
 using namespace std;
 using namespace Test;
 
+void
+Test::Neighbor::ice_print(ostream& os) const
+{
+    os << name;
+    if (age)
+    {
+        os << " (" << *age << ")";
+    }
+    os << " @ " << address;
+}
+
 template<class T>
 void
 testPrint(const T& value, const string& expected, std::optional<int> floatPrecision = std::nullopt)
@@ -91,6 +102,16 @@ testClass()
         "= []}");
 }
 
+void
+testClassCustomPrint()
+{
+    auto neighbor = make_shared<Neighbor>("Alice", 30, "123 Main St");
+    testPrint(neighbor, "Alice (30) @ 123 Main St");
+
+    // This works too:
+    testPrint(*neighbor, "Alice (30) @ 123 Main St");
+}
+
 void
 allTests(Test::TestHelper*)
 {
@@ -99,4 +120,5 @@ allTests(Test::TestHelper*)
     testCustomStruct();
     testDictionaryStruct();
     testClass();
+    testClassCustomPrint();
 }

cpp/test/Ice/print/Test.ice

@@ -58,4 +58,10 @@ module Test
         Employee manager;
         EmployeeSeq directReports;
     }
+
+    ["cpp:custom-print"]
+    class Neighbor extends Person
+    {
+        string address;
+    }
 }