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 an
// ExtensionRegistry 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 *Root classes provide +extensionRegistry for the extensions defined in a
// given file *and* all files it imports.  You can also create a
// GPBExtensionRegistry, and merge those registries to handle parsing extensions
// defined from non overlapping files.
//
//    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];
//
@interface GPBExtensionRegistry : NSObject<NSCopying>

- (void)addExtension:(GPBExtensionDescriptor *)extension;
- (void)addExtensions:(GPBExtensionRegistry *)registry;

- (nullable GPBExtensionDescriptor *)extensionForDescriptor:(GPBDescriptor *)descriptor
                                                fieldNumber:(NSInteger)fieldNumber;

@end

NS_ASSUME_NONNULL_END