#import "CollapsingFutures.h"

// ask for the address book, which is asynchronous because IOS may ask the user to allow it
TOCFuture *futureAddressBook = SomeUtilityClass.asyncGetAddressBook;

// if the user refuses access to the address book (or something else goes wrong), log the problem
[futureAddressBook catchDo:^(id error) {
    NSLog("There was an error (%@) getting the address book.", error);
}];

// if the user allowed access, use the address book
[futureAddressBook thenDo:^(id arcAddressBook) {
    ABAddressBookRef addressBook = (__bridge ABAddressBookRef)arcAddressBook;

    ... do stuff with addressBook ...
}];

#import "CollapsingFutures.h"

+(TOCFuture *) asyncGetAddressBook {
    CFErrorRef creationError = nil;
    ABAddressBookRef addressBookRef = ABAddressBookCreateWithOptions(NULL, &creationError);

    // did we fail right away? Then return an already-failed future
    if (creationError != nil) {
        return [TOCFuture futureWithFailure:(__bridge_transfer id)creationError];
    }

    // we need to make an asynchronous call, so we'll use a future source
    // that way we can return its future right away and fill it in later
    TOCFutureSource *resultSource = [FutureSource new];

    id arcAddressBook = (__bridge_transfer id)addressBookRef; // retain the address book in ARC land
    ABAddressBookRequestAccessWithCompletion(addressBookRef, ^(bool granted, CFErrorRef requestAccessError) {
        // time to fill in the future we returned
        if (granted) {
            [resultSource trySetResult:arcAddressBook];
        } else {
            [resultSource trySetFailure:(__bridge id)requestAccessError];
        }
    });

    return resultSource.future;
}

#import "CollapsingFutures.h"

+(TOCFuture *) sumOfFutures:(NSArray*)arrayOfFuturesOfNumbers {
    // we want all of the values to be ready before we bother summing
    TOCFuture* futureOfArrayOfNumbers = arrayOfFuturesOfNumbers.toc_thenAll;

    // once the array of values is ready, add up its entries to get the sum
    TOCFuture* futureSum = [futureOfArrayOfNumbers then:^(NSArray* numbers) {
        double total = 0;
        for (NSNumber* number in numbers) {
            total += number.doubleValue;
        }
        return @(total);
    }];

    // this future will eventually contain the sum of the eventual numbers in the input array
    // if any of the evetnual numbers fails, this future will end up failing as well
    return futureSum;
}