protobuf/objectivec/GPBExtensionRegistry.h

// Protocol Buffers - Google's data interchange format
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#import <Foundation/Foundation.h>

@class GPBDescriptor;
@class GPBExtensionDescriptor;

NS_ASSUME_NONNULL_BEGIN

/// A table of known extensions, searchable by name or field number.  When
/// parsing a protocol message that might have extensions, you must provide a
/// @c GPBExtensionRegistry in which you have registered any extensions that you
/// want to be able to parse. Otherwise, those extensions will just be treated
/// like unknown fields.
///
/// The @c *Root classes provide @c +extensionRegistry for the extensions defined
/// in a given file *and* all files it imports. You can also create a
/// @c GPBExtensionRegistry, and merge those registries to handle parsing
/// extensions defined from non overlapping files.
///
/// @code
/// GPBExtensionRegistry *registry =
///     [[[MyProtoFileRoot extensionRegistry] copy] autorelease];
/// [registry addExtension:[OtherMessage neededExtension];  // Not in MyProtoFile
/// NSError *parseError = nil;
/// MyMessage *msg = [MyMessage parseData:data
///                     extensionRegistry:registry
///                                 error:&parseError];
/// @endcode
@interface GPBExtensionRegistry : NSObject<NSCopying>

/// Add the given @c GPBExtensionDescriptor to this registry.
///
/// @param extension The extension description to add.
- (void)addExtension:(GPBExtensionDescriptor *)extension;

/// Adds all the extensions from another registry to this registry.
///
/// @param registry The registry to merge into this registry.
- (void)addExtensions:(GPBExtensionRegistry *)registry;

/// Looks for the extension registered for the given field number on a given
/// @c GPBDescriptor.
///
/// @param descriptor  The descriptor to look for a registered extension on.
/// @param fieldNumber The field number of an extension to look for.
///
/// @return The registered @c GPBExtensionDescripto or nil if none was found.
- (nullable GPBExtensionDescriptor *)extensionForDescriptor:(GPBDescriptor *)descriptor
                                                fieldNumber:(NSInteger)fieldNumber;

@end

NS_ASSUME_NONNULL_END