@ -21,6 +21,7 @@
# include <cstdint>
# include <iosfwd>
# include <string>
# include <type_traits>
# include "absl/base/attributes.h"
# include "absl/log/absl_check.h"
@ -53,6 +54,7 @@ class FastReflectionStringSetter;
class Reflection ;
class Descriptor ;
class AssignDescriptorsHelper ;
class MessageLite ;
namespace io {
@ -120,6 +122,9 @@ class PROTOBUF_EXPORT CachedSize {
# endif
} ;
// For MessageLite to friend.
class TypeId ;
class SwapFieldHelper ;
// See parse_context.h for explanation
@ -638,6 +643,15 @@ class PROTOBUF_EXPORT MessageLite {
// return a default table instead of a unique one.
virtual const ClassData * GetClassData ( ) const = 0 ;
template < typename T >
static auto GetClassDataGenerated ( ) {
// We could speed this up if needed by avoiding the function call.
// In LTO this is likely inlined, so it might not matter.
static_assert (
std : : is_same < const T & , decltype ( T : : default_instance ( ) ) > : : value , " " ) ;
return T : : default_instance ( ) . T : : GetClassData ( ) ;
}
internal : : InternalMetadata _internal_metadata_ ;
// Return the cached size object as described by
@ -682,6 +696,7 @@ class PROTOBUF_EXPORT MessageLite {
friend class internal : : LazyField ;
friend class internal : : SwapFieldHelper ;
friend class internal : : TcParser ;
friend class internal : : TypeId ;
friend class internal : : WeakFieldMap ;
friend class internal : : WireFormatLite ;
@ -717,6 +732,32 @@ class PROTOBUF_EXPORT MessageLite {
namespace internal {
// A typeinfo equivalent for protobuf message types. Used for
// DynamicCastToGenerated.
// We might make this class public later on to have an alternative to
// `std::type_info` that works when RTTI is disabled.
class TypeId {
public :
constexpr explicit TypeId ( const MessageLite : : ClassData * data ) : data_ ( data ) { }
friend constexpr bool operator = = ( TypeId a , TypeId b ) {
return a . data_ = = b . data_ ;
}
friend constexpr bool operator ! = ( TypeId a , TypeId b ) { return ! ( a = = b ) ; }
static TypeId Get ( const MessageLite & msg ) {
return TypeId ( msg . GetClassData ( ) ) ;
}
template < typename T >
static TypeId Get ( ) {
return TypeId ( MessageLite : : GetClassDataGenerated < T > ( ) ) ;
}
private :
const MessageLite : : ClassData * data_ ;
} ;
template < bool alias >
bool MergeFromImpl ( absl : : string_view input , MessageLite * msg ,
const internal : : TcParseTableBase * tc_table ,
@ -820,6 +861,83 @@ T* OnShutdownDelete(T* p) {
std : : string ShortFormat ( const MessageLite & message_lite ) ;
std : : string Utf8Format ( const MessageLite & message_lite ) ;
// Tries to downcast this message to a generated message type. Returns nullptr
// if this class is not an instance of T. This works even if RTTI is disabled.
//
// This also has the effect of creating a strong reference to T that will
// prevent the linker from stripping it out at link time. This can be important
// if you are using a DynamicMessageFactory that delegates to the generated
// factory.
template < typename T >
const T * DynamicCastToGenerated ( const MessageLite * from ) {
static_assert ( std : : is_base_of < MessageLite , T > : : value , " " ) ;
internal : : StrongReferenceToType < T > ( ) ;
// We might avoid the call to T::GetClassData() altogether if T were to
// expose the class data pointer.
if ( from = = nullptr | |
internal : : TypeId : : Get < T > ( ) ! = internal : : TypeId : : Get ( * from ) ) {
return nullptr ;
}
return static_cast < const T * > ( from ) ;
}
template < typename T >
const T * DynamicCastToGenerated ( const MessageLite * from ) ;
template < typename T >
T * DynamicCastToGenerated ( MessageLite * from ) {
return const_cast < T * > (
DynamicCastToGenerated < T > ( static_cast < const MessageLite * > ( from ) ) ) ;
}
// An overloaded version of DynamicCastToGenerated for downcasting references to
// base Message class. If the argument is not an instance of T, it terminates
// with an error.
template < typename T >
const T & DynamicCastToGenerated ( const MessageLite & from ) {
const T * destination_message = DynamicCastToGenerated < T > ( & from ) ;
ABSL_CHECK ( destination_message ! = nullptr )
< < " Cannot downcast " < < from . GetTypeName ( ) < < " to "
< < T : : default_instance ( ) . GetTypeName ( ) ;
return * destination_message ;
}
template < typename T >
T & DynamicCastToGenerated ( MessageLite & from ) {
return const_cast < T & > (
DynamicCastToGenerated < T > ( static_cast < const MessageLite & > ( from ) ) ) ;
}
// A lightweight function for downcasting base MessageLite pointer to derived
// type. It should only be used when the caller is certain that the argument is
// of instance T and T is a generated message type.
template < typename T >
const T * DownCastToGenerated ( const MessageLite * from ) {
internal : : StrongReferenceToType < T > ( ) ;
ABSL_DCHECK ( DynamicCastToGenerated < T > ( from ) = = from )
< < " Cannot downcast " < < from - > GetTypeName ( ) < < " to "
< < T : : default_instance ( ) . GetTypeName ( ) ;
return static_cast < const T * > ( from ) ;
}
template < typename T >
T * DownCastToGenerated ( MessageLite * from ) {
return const_cast < T * > (
DownCastToGenerated < T > ( static_cast < const MessageLite * > ( from ) ) ) ;
}
template < typename T >
const T & DownCastToGenerated ( const MessageLite & from ) {
return * DownCastToGenerated < T > ( & from ) ;
}
template < typename T >
T & DownCastToGenerated ( MessageLite & from ) {
return * DownCastToGenerated < T > ( & from ) ;
}
} // namespace protobuf
} // namespace google
Protobuf Team Bot
8 months ago
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