I make heavy use of protocols and inheritance in one of my projects. My subclasses often define a more specific delegate protocol than their superclass, and make their own delegate protocol conform to the protocols of the superclass' delegate.
When a project compiled with clang imports one of these header chains, the compiler complains that the declaration of the subclass' delegate property is incompatible with the superclass' declaration.
I have noted that this only occurs when the protocols are forward declared using @protocol, and later defined. I like to forward declare my @protocols and define them after my @interface declaration.
Example Warning Given:
warning: property type 'id<AFNetworkTransportControlDelegate,AFNetworkTransportDataDelegate>' is incompatible with type 'id<AFNetworkConnectionLayerControlDelegate,AFNetworkConnectionLayerDataDelegate>' inherited from 'AFNetworkConnectionLayer' [3]
Expected Results:
Don't warn about property type incompatibilities when basing the warning on a forward declared @protocol, the compiler should read ahead to the @protocol definition before issuing a warning.
Workaround:
Define the @protocol before the class that uses the declaration in it's property list, using @class to forward declare the class if necessary.
Example Project:
Attached is an archive with two files.
To demonstrate the warning illustrated above, compile with no additional defines:
clang clang_protocol_conformance.m -framework Foundation
and receive the following warning:
clang_protocol_conformance.m:19:35: warning: property type 'id' is incompatible with type 'id' inherited from 'Parent'
@property (assign) id delegate;
^
1 warning generated.
To workaround the problem, define RM_FORWARD_DEFINE_PROTOCOLS, which moves the #import above the @interface declarations, and fixes the warnings.
Compile with:
clang clang_protocol_conformance.m -framework Foundation -DRM_FORWARD_DEFINE_PROTOCOLS
and no warnings are generated.
Clang Version:
Apple clang version 2.1 (tags/Apple/clang-163.7.1) (based on LLVM 3.0svn)
Target: x86_64-apple-darwin11.0.0
Thread model: posix
llvmbot
commented
11 years ago
Extended Description
Summary:
I make heavy use of protocols and inheritance in one of my projects. My subclasses often define a more specific delegate protocol than their superclass, and make their own delegate protocol conform to the protocols of the superclass' delegate.
When a project compiled with clang imports one of these header chains, the compiler complains that the declaration of the subclass' delegate property is incompatible with the superclass' declaration.
I have noted that this only occurs when the protocols are forward declared using @protocol, and later defined. I like to forward declare my @protocols and define them after my @interface declaration.
Example Warning Given:
warning: property type 'id<AFNetworkTransportControlDelegate,AFNetworkTransportDataDelegate>' is incompatible with type 'id<AFNetworkConnectionLayerControlDelegate,AFNetworkConnectionLayerDataDelegate>' inherited from 'AFNetworkConnectionLayer' [3]
Expected Results:
Don't warn about property type incompatibilities when basing the warning on a forward declared @protocol, the compiler should read ahead to the @protocol definition before issuing a warning.
Workaround:
Define the @protocol before the class that uses the declaration in it's property list, using @class to forward declare the class if necessary.
Example Project:
Attached is an archive with two files.
To demonstrate the warning illustrated above, compile with no additional defines:
clang clang_protocol_conformance.m -framework Foundationand receive the following warning:
clang_protocol_conformance.m:19:35: warning: property type 'id' is incompatible with type 'id' inherited from 'Parent'
@property (assign) id delegate;
^
1 warning generated.
To workaround the problem, define RM_FORWARD_DEFINE_PROTOCOLS, which moves the #import above the @interface declarations, and fixes the warnings.
Compile with:
clang clang_protocol_conformance.m -framework Foundation -DRM_FORWARD_DEFINE_PROTOCOLSand no warnings are generated.
Clang Version:
Apple clang version 2.1 (tags/Apple/clang-163.7.1) (based on LLVM 3.0svn) Target: x86_64-apple-darwin11.0.0 Thread model: posix