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Example/Pods/ReactiveObjC/ReactiveObjC/RACEmptySequence.m

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+//
+//  RACEmptySequence.m
+//  ReactiveObjC
+//
+//  Created by Justin Spahr-Summers on 2012-10-29.
+//  Copyright (c) 2012 GitHub. All rights reserved.
+//
+
+#import "RACEmptySequence.h"
+
+@implementation RACEmptySequence
+
+#pragma mark Lifecycle
+
++ (instancetype)empty {
+	static id singleton;
+	static dispatch_once_t pred;
+
+	dispatch_once(&pred, ^{
+		singleton = [[self alloc] init];
+	});
+
+	return singleton;
+}
+
+#pragma mark RACSequence
+
+- (id)head {
+	return nil;
+}
+
+- (RACSequence *)tail {
+	return nil;
+}
+
+- (RACSequence *)bind:(RACStreamBindBlock)bindBlock passingThroughValuesFromSequence:(RACSequence *)passthroughSequence {
+	return passthroughSequence ?: self;
+}
+
+#pragma mark NSCoding
+
+- (Class)classForCoder {
+	// Empty sequences should be encoded as themselves, not array sequences.
+	return self.class;
+}
+
+- (instancetype)initWithCoder:(NSCoder *)coder {
+	// Return the singleton.
+	return self.class.empty;
+}
+
+- (void)encodeWithCoder:(NSCoder *)coder {
+}
+
+#pragma mark NSObject
+
+- (NSString *)description {
+	return [NSString stringWithFormat:@"<%@: %p>{ name = %@ }", self.class, self, self.name];
+}
+
+- (NSUInteger)hash {
+	// This hash isn't ideal, but it's better than -[RACSequence hash], which
+	// would just be zero because we have no head.
+	return (NSUInteger)(__bridge void *)self;
+}
+
+- (BOOL)isEqual:(RACSequence *)seq {
+	return (self == seq);
+}
+
+@end