tags	languages
blocks, NSArray	objc

#ArrayBlocks

Instructions

Apple has provided us with some great functionality in the NSArray class that we haven't touched on just yet. For example, the method enumerateObjectsUsingBlock: gives us quite of flexibility to do a lot with the objects in an array, with fewer lines of code. Similarly, Apple provides us some advanced functionality for filtering collections such as NSArray with its predicateUsingBlock: method.

Let's take a look at an example of each of these.

######Example

[testArray enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
	NSLog(@"%@",@([(NSNumber *)obj integerValue] + 1));
}];

Here we have created an implementation of enumerateObjectsUsingBlock that will return each numeric value in our NSArray with that number plus one. (Be careful: This block does not consider the possibility that your array contains objects that do not conform to the method integerValue!)

######Example

[NSPredicate *evenPredicate = [NSPredicate predicateWithBlock:^BOOL(id evaluatedObject, NSDictionary *bindings){
        return ([evaluatedObject integerValue]%2 == 0);
    }];
    
NSArray *filteredResultsArrayTwo = [resultsArray filteredArrayUsingPredicate:evenPredicate];

Here we have created a predicate that will return only even numbers of our array. Same as above: Be careful. This block does not consider the possibility that your array contains objects that do not conform to the method integerValue!

Now it is your turn: Try writing your own methods that take blocks of code to mimic the capabilities of these two functions for NSArray objects. Your methods should extend the NSArray class (via a category) and will be called mapWithOperation: (our form of enumerateObjectsUsingBlock:) and selectWithComparator: (our form of predicateUsingBlock:). The arguments should be the blocks.

Two additional notes:

1. For our equivalent of enumerateObjectsUsingBlock do not concern yourself with adding in the BOOL* argument for the basic version.

2. There are no tests for this lab; so in order to know it has worked, make sure you try running you methods with some dummy data of your own.

3. selectWithComparitor should be built as an instance method, not a class method like predicateWithBlock.

Go!

##Advanced Now add in the BOOL* argument for mapWithOperation:. Note: This will not further your understanding of blocks, but it will teach you a little bit more about memory addresses.