Apples And Holidays

Objectives

1. Use NSPredicate to filter objects in an array.
2. Practice accessing a nested collection.

Instructions

In the FISAppDelegate.h header file, declare the following seven instance methods, then navigate to the FISAppDelegate.m implementation file and define them all to either return nil or return a test object of the correct kind:

• pickApplesFromFruits: which takes one NSArray argument fruits and returns an NSArray.

• holidaysInSeason:inDatabase: which takes two arguments, an NSString called season and an NSDictionary called database, and returns an NSArray.

• suppliesInHoliday:inSeason:inDatabase: which takes three arguments: an NSString called holiday, an NSString called season, and an NSDictionary called database; and returns an NSArray.

• holiday:isInSeason:inDatabase: which takes three arguments: an NSString called holiday, an NSString called season, and an NSDictionary called database; and returns a BOOL.

• supply:isInHoliday:inSeason:inDatabase: which takes four arguments: an NSString called supply, an NSString called holiday, an NSString called season, and an NSDictionary called database; and returns a BOOL.

• addHoliday:toSeason:inDatabase: which takes three arguments: an NSString called holiday, an NSString called season, and an NSDictionary called database; and returns an NSDictionary.

• addSupply:toHoliday:inSeason:inDatabase: which takes four arguments: an NSString called supply, an NSString called holiday, an NSString called season, and an NSDictionary called database; and returns an NSDictionary.

Top-tip: Hitting enter while you cursor is in the space between the argument components in a method declaration line will align the components of the method name by the : ("colon") on a new line.

Run the tests with ⌘``U to see that most of them fail.

Apple Picker

And I keep hearing from the cellar bin
The rumbling sound
Of load on load of apples coming in.
—After Apple Picking, Robert Frost

Write out the implementation body for the pickApplesFromFruits: method so that it returns an NSArray of all of the occurrences of the string @"apple" in the argument array fruits. Think about how you can filter the argument array using NSPredicate.

Hint: Use the self keypath when filtering an array of strings.

Holiday Supplies

1. Look at the HolidayTests file to review the structure of the suppliesByHolidayAndSeason dictionary at the top of the file. This dictionary is submitted to the database argument of the method calls across the test file, meaning that it's the collection you'll be working with. You should be able to decipher that this is a nested collection: the first layer is a static dictionary of "season" keys; each season key is bound to a mutable dictionary of "holiday" keys; each holiday key is bound to mutable array of "supplies" relevant to that holiday.
2. Write the implementations for the rest of the methods, running the tests as you finish each one to make sure its tests pass:

• holidaysInSeason:inDatabase: to return an array of all of the "holiday" keys in the sub-dictionary associated with the submitted "season" argument.

• suppliesInHoliday:inSeason:inDatabase: to return the mutable array of all of the supplies for the submitted "holiday" in the submitted "season".

• holiday:isInSeason:inDatabase: to return whether or not the submitted "season" contains a key that matches the "holiday" argument.

• supply:isInHoliday:inSeason:inDatabase: to return whether or not the submitted "holiday" in the submitted "season" contains in its array the submitted "supply" string.

• addHoliday:toSeason:inDatabase: to create a new key-value pair in the submitted "season" key's sub-dictionary that uses the submitted "holiday" as the key and sets up an empty mutable array as its value.

• addSupply:toHoliday:inSeason:inDatabase: to insert the submitted "supply" argument into the mutable array of the submitted "holiday" key in the sub-dictionary of the submitted "season" key.

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