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guard sourceUrl.matches([".dat", ".csv"]) else {
  print("Extension not allowed!")
}

// do your stuff here

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The introduction to Reactive Programming you've been missing

(by @andrestaltz)

---

This tutorial as a series of videos

If you prefer to watch video tutorials with live-coding, then check out this series I recorded with the same contents as in this article: Egghead.io - Introduction to Reactive Programming.

---

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//
//  MGNavigationTransitioningDelegate 
//
//  Created by Philip Vasilchenko on 27.11.13.
//

#import <UIKit/UIKit.h>


@interface MGNavigationTransitioningDelegate : NSObject <UINavigationControllerDelegate>

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// CDBaseManagedObject.h
@interface CDBaseManagedObject : NSManagedObject
 
+ (NSString *)entityName;
+ (instancetype)insertNewObjectIntoContext:(NSManagedObjectContext *)context;
 
@end
 
// CDBaseManagedObject.m
@implementation CDBaseManagedObject

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// NSManagedObject+CDAdditions.h
@interface NSManagedObject (CDAdditions)
 
+ (NSString *)CDAdditionsEntityName;
+ (instancetype)CDAdditionsInsertNewObjectIntoContext:(NSManagedObjectContext *)context;
 
@end
 
// NSManagedObject+CDAdditions.m
@implementation NSManagedObject (CDAdditions)

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// how to use NetworkRequest class
NSURL *urlRequest = [NSURL URLWithString:@"someurlhere"];
NetworkRequest *request = [[NetworkRequest alloc] initWithURL:urlRequest];
[request performWithCompletionHandler:^(NSData *data) {
    NSLog(@"Hello world!!!");
}];

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// NetworkRequest.h
typedef void(^NetworkRequestCompletionHandler)(NSData *data);

@interface NetworkRequest : NSObject

@property (nonatomic, strong, readonly) NSURL* url;

- (id)initWithURL:(NSURL*)url;
- (void)performWithCompletionHandler:(NetworkRequestCompletionHandler)completionHandler

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// in NetworkFetcher class
- (void)requestCompleted {
    if(self.completionHandler) {
        // invoke the block with data
        self.completionHandler(self.downloadedData);
    }

    // break the retain cycle
    self.completionHandler = nil;
}

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- (void)downloadData {
    NSURL *url = [NSURL URLWithString:@"someurlhere"];
    NetworkFetcher *networkFetcher = [[NetworkFetcher alloc] initWithURL:url];
    [networkFetcher startWithCompletionHandler:^(NSData *data){
        NSLog(@"Request URL %@ finished", networkFetcher.url);
        _fetchedData = data;
    }];
}

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// how to use NSArray+FAPMap category
NSArray* toMapArray = @[@1, @2, @3];
NSArray* mappedArray = [toMapArray fap_map:^id(id item) {
    NSNumber* itemAsNumber = (NSNumber*)item;
    int resultValue = [itemAsNumber integerValue] * 3;
    return @(resultValue);
}];