Formal protocol conformance in BoxUtil

Author: gershnik

CHANGELOG.md

@@ -5,6 +5,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 ## Unreleased
 
+### Added
+- Boxed values now actually formally conform to relevant protocols (as reported by `confromsToProtocol:`)
+
 ### Fixed
 - Added `<exception>` header include to XCTestUtil.h that is now required on newer Xcodes
 - Making `BoxUtil.h` not rely on `std::filesystem` which is not available on older Apple

include/objc-helpers/BoxUtil.h

@@ -167,6 +167,9 @@ class __attribute__((visibility("hidden"))) BoxMaker {
             std::string className = objcData.modulePrefix + "Boxed["s + tid.name() + ']';
             Class cls = objc_allocateClassPair(objcData.NSObjectClass, className.c_str(), 0);
             classData.cls = cls;
+
+            if (!class_addProtocol(cls, @protocol(BoxedValue)))
+                    @throw [NSException exceptionWithName:NSGenericException reason:@"class_addProtocol(@protocol(NSCopying)) failed" userInfo:nullptr];
 
             if (!class_addIvar(cls, "_value", sizeof(T), alignof(T), @encode(T)))
                 @throw [NSException exceptionWithName:NSGenericException reason:@"class_addIvar(_value) failed" userInfo:nullptr];
@@ -185,6 +188,9 @@ class __attribute__((visibility("hidden"))) BoxMaker {
             if constexpr (std::is_copy_constructible_v<T>) {
                 if (!class_addMethod(cls, objcData.copyWithZoneSel, IMP(copyWithZone), "@@:@"))
                     @throw [NSException exceptionWithName:NSGenericException reason:@"class_addMethod(copyWithZone) failed" userInfo:nullptr];
+
+                if (!class_addProtocol(cls, @protocol(NSCopying)))
+                    @throw [NSException exceptionWithName:NSGenericException reason:@"class_addProtocol(@protocol(NSCopying)) failed" userInfo:nullptr];
             }
 
             if (!class_addMethod(cls, objcData.isEqualSel, IMP(isEqual), "@@:@"))
@@ -196,6 +202,8 @@ class __attribute__((visibility("hidden"))) BoxMaker {
             if constexpr (std::totally_ordered<T>) {
                 if (!class_addMethod(cls, objcData.compareSel, IMP(compare), (@encode(NSComparisonResult) + "@:@"s).c_str()))
                     @throw [NSException exceptionWithName:NSGenericException reason:@"class_addMethod(compare) failed" userInfo:nullptr];
+                if (!class_addProtocol(cls, @protocol(BoxedComparable)))
+                    @throw [NSException exceptionWithName:NSGenericException reason:@"class_addProtocol(@protocol(BoxedComparable)) failed" userInfo:nullptr];
             }
 
             objc_registerClassPair(cls);

test/BoxUtilTests.mm

@@ -12,6 +12,11 @@
     CHECK([obj.description isEqualToString:@"42"]);
     CHECK(obj.hash == std::hash<int>()(42));
 
+    CHECK([obj conformsToProtocol:@protocol(NSCopying)]);
+    CHECK([obj conformsToProtocol:@protocol(BoxedValue)]);
+    CHECK([obj conformsToProtocol:@protocol(BoxedComparable)]);
+    CHECK([obj conformsToProtocol:@protocol(NSObject)]);
+    
     @try {
         boxedValue<long>(obj);
         FAIL("able to unbox wrong type");
@@ -71,6 +76,12 @@
 
     auto obj = box(std::string("abc"));
     static_assert(std::is_same_v<decltype(obj), NSObject<BoxedValue, BoxedComparable, NSCopying> *>);
+    
+    CHECK([obj conformsToProtocol:@protocol(NSCopying)]);
+    CHECK([obj conformsToProtocol:@protocol(BoxedValue)]);
+    CHECK([obj conformsToProtocol:@protocol(BoxedComparable)]);
+    CHECK([obj conformsToProtocol:@protocol(NSObject)]);
+    
     CHECK(boxedValue<std::string>(obj) == str);
     CHECK([obj.description isEqualToString:@"abc"]);
     CHECK(obj.hash == std::hash<std::string>()(str));
@@ -93,6 +104,12 @@
 
     auto obj = box(std::make_unique<int>(5));
     static_assert(std::is_same_v<decltype(obj), NSObject<BoxedValue, BoxedComparable> *>);
+    
+    CHECK(![obj conformsToProtocol:@protocol(NSCopying)]);
+    CHECK([obj conformsToProtocol:@protocol(BoxedValue)]);
+    CHECK([obj conformsToProtocol:@protocol(BoxedComparable)]);
+    CHECK([obj conformsToProtocol:@protocol(NSObject)]);
+    
     CHECK(*boxedValue<std::unique_ptr<int>>(obj) == 5);
 
     @try {
@@ -143,6 +160,11 @@
 
     static_assert(std::is_same_v<decltype(obj1), NSObject<BoxedValue, NSCopying> *>);
 
+    CHECK([obj1 conformsToProtocol:@protocol(NSCopying)]);
+    CHECK([obj1 conformsToProtocol:@protocol(BoxedValue)]);
+    CHECK(![obj1 conformsToProtocol:@protocol(BoxedComparable)]);
+    CHECK([obj1 conformsToProtocol:@protocol(NSObject)]);
+    
     CHECK(boxedValue<foo>(obj1).i == 4);
     CHECK(boxedValue<foo>(obj2).c == 'b');
     CHECK([obj1 isEqual:obj2]);