Implement QPDFObjectHandle equality

ChangeLog

@@ -1,5 +1,9 @@
 2022-09-06  Jay Berkenbilt  <ejb@ql.org>
 
+        * Add == equality for QPDFObjectHandle. Two QPDFObjectHandle
+        objects are equal if they point to the same underlying object,
+        meaning changes to one will be reflected in the other.
+
         * The --show-encryption option now works even if a correct
         password is not supplied. If you were using --show-encryption to
         test whether you have the right password, use --requires-password

include/qpdf/QPDFObjectHandle.hh

@@ -334,6 +334,15 @@ class QPDFObjectHandle
     QPDF_DLL
     inline bool isInitialized() const;
 
+    // Two QPDFObjectHandle objects are equal if they point to exactly
+    // the same underlying object, meaning that changes to one are
+    // reflected in the other, or "if you paint one, the other one
+    // changes color."
+    QPDF_DLL
+    bool operator==(QPDFObjectHandle const&) const;
+    QPDF_DLL
+    bool operator!=(QPDFObjectHandle const&) const;
+
     // Return type code and type name of underlying object.  These are
     // useful for doing rapid type tests (like switch statements) or
     // for testing and debugging.

libqpdf/QPDFObjectHandle.cc

@@ -236,6 +236,18 @@ LastChar::getLastChar()
     return this->last_char;
 }
 
+bool
+QPDFObjectHandle::operator==(QPDFObjectHandle const& rhs) const
+{
+    return this->obj == rhs.obj;
+}
+
+bool
+QPDFObjectHandle::operator!=(QPDFObjectHandle const& rhs) const
+{
+    return this->obj != rhs.obj;
+}
+
 qpdf_object_type_e
 QPDFObjectHandle::getTypeCode()
 {

manual/release-notes.rst

@@ -208,6 +208,11 @@ For a detailed list of changes, please see the file
       generally not happen for correct code, but at least the
       situation is detectible now.
 
+    - It is now possible to test ``QPDFObjectHandle`` equality with
+      ``==`` and ``!=``. Two ``QPDFObjectHandle`` objects are equal if
+      they point to the same underlying object, meaning changes to one
+      will be reflected in the other.
+
     - Add new factory method ``QPDF::create()`` that returns a
       ``std::shared_ptr<QPDF>``.
 

qpdf/qtest/object-handle-api.test

@@ -14,8 +14,6 @@ cleanup();
 
 my $td = new TestDriver('object-handle-api');
 
-my $n_tests = 2;
-
 $td->runtest("dictionary keys",
              {$td->COMMAND => "test_driver 87 - -"},
              {$td->STRING => "test 87 done\n", $td->EXIT_STATUS => 0},
@@ -24,6 +22,10 @@ $td->runtest("fluent interfaces",
              {$td->COMMAND => "test_driver 88 minimal.pdf -"},
              {$td->FILE => "test88.out", $td->EXIT_STATUS => 0},
              $td->NORMALIZE_NEWLINES);
+$td->runtest("equality",
+             {$td->COMMAND => "test_driver 93 minimal.pdf -"},
+             {$td->STRING => "test 93 done\n", $td->EXIT_STATUS => 0},
+             $td->NORMALIZE_NEWLINES);
 
 cleanup();
-$td->report($n_tests);
+$td->report(3);

qpdf/test_driver.cc

@@ -3275,6 +3275,33 @@ test_92(QPDF& pdf, char const* arg2)
     assert(!root.isIndirect());
 }
 
+static void
+test_93(QPDF& pdf, char const* arg2)
+{
+    // Test QPDFObjectHandle equality. Two QPDFObjectHandle objects
+    // are equal if they point to the same underlying object.
+
+    auto trailer = pdf.getTrailer();
+    auto root1 = trailer.getKey("/Root");
+    auto root2 = pdf.getRoot();
+    assert(root1 == root2);
+    auto oh1 = "<< /One /Two >>"_qpdf;
+    auto oh2 = oh1;
+    assert(oh1 == oh2);
+    auto oh3 = "<< /One /Two >>"_qpdf;
+    assert(oh1 != oh3);
+    oh2.replaceKey("/One", "/Three"_qpdf);
+    assert(oh1 == oh2);
+    assert(oh2.unparse() == "<< /One /Three >>");
+    assert(!oh1.isIndirect());
+    auto oh4 = pdf.makeIndirectObject(oh1);
+    assert(oh1 == oh4);
+    assert(oh1.isIndirect());
+    assert(oh4.isIndirect());
+    trailer.replaceKey("/Potato", oh1);
+    assert(trailer.getKey("/Potato") == oh2);
+}
+
 void
 runtest(int n, char const* filename1, char const* arg2)
 {
@@ -3384,7 +3411,7 @@ runtest(int n, char const* filename1, char const* arg2)
         {80, test_80}, {81, test_81}, {82, test_82}, {83, test_83},
         {84, test_84}, {85, test_85}, {86, test_86}, {87, test_87},
         {88, test_88}, {89, test_89}, {90, test_90}, {91, test_91},
-        {92, test_92}};
+        {92, test_92}, {93, test_93}};
 
     auto fn = test_functions.find(n);
     if (fn == test_functions.end()) {