Hello everyone,
Clang now provides an option -fobjc-encode-cxx-class-template-spec /
-fno-objc-encode-cxx-class-template-spec to specify whether encodings
that include C++ types with template parameters should be mangled in
full or abbreviated to ^v. This is an ABI-breaking flag for the GNUstep
ABI, where type encodings are used both in dispatch lookup and in ivar
offset variables. If you have an Objective-C++ codebase that uses a lot
of template instantiations, this will give you smaller binaries. It is
safe to use *only* if you do not expose ivars or methods in your public
headers that include templated C++ types.
For example, this is safe:
public_header.h
```obj-c
@interface UnorderedStringMap
- (id)objectForKey: (NSString*)aKey;
@end
```
private.m:
```obj-c
@implementation UnorderedStringMap
{
@private
std::unordered_map<NSString*, id> map;
}
- (id)objectForKey: (NSString*)aKey
{
return map[aKey];
}
@end
```
This is not:
public_header.h
```obj-c
@interface UnorderedStringMap
{
@public:
// ivar can't be found if the flag differs between two compilation units
std::unordered_map<NSString*, id> map;
}
- (id)objectForKey: (NSString*)aKey;
// Method can't be called if the flag differs between two compilation units.
- (void)resetMap: (std::unordered_map<NSString*, id>&&)aMap;
@end
```
If you use Objective-C++ internally but expose only Objective-C
interfaces, then you may find this flag useful.
David
