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Working With Mutable Collections

The collection opaque types CFArray, CFDictionary, CFSet, and CFBag offer similar sets of functions for manipulating the values contained by mutable collections: adding values, removing values, replacing values, and so on. There are some differences in behavior based on whether the collection ensures the uniqueness of keys and values. Table 1 summaries the behavior of the mutability functions. The Operation column identifies the type of operation using the parameter found in a mutability function, such as “Replace” in CFDictionaryReplaceValue.

**Table 1** Semantics of mutable collection operations
Operation	Collection Type	What it Means
Append	CFArray	Insert the value after all other values (index=count).
Insert	CFArray	Insert the value at the given index of the collection.
Add	all except CFArray	For CFDictionary and CFSet, add value if it is absent, do nothing if it is present. For CFBag, add value even if it is already present.
Replace	all	If the specified value is present, replace it with another value; otherwise, do nothing.
Set	all	Add the value if it is absent, replace it if it is present.
Remove	all	Remove the value if it is present, do nothing if it is absent.

With fixed-size mutable collections, you must take care to avoid adding beyond the capacity limit. A fixed-size collection will let you add as many values as you want, but gives no notice when you exceed the capacity. However, doing so will result in undefined behavior that is most likely undesirable.

The CFArray type features one mutability operation that is special to it. With the CFArraySortValues function you can sort the values contained by the array. A comparator function, which must conform to the CFComparatorFunction type, is used to compare values. Listing 1 gives an example of the use of the CFArraySortValues function.

Listing 1 Sorting an array

CFMutableArrayRef createSortedArray(CFArrayRef anArray) {

    CFIndex count = CFArrayGetCount(anArray);

    CFMutableArrayRef marray = CFArrayCreateMutableCopy(NULL, count, anArray);

    CFArraySortValues(marray, CFRangeMake(0, count), (CFComparatorFunction)CFStringCompare, NULL);

    return marray;

Notice that the CFStringCompare function is used, in this case, to compare CFString objects. Core Foundation provides other comparator functions that are of the CFComparatorFunction type, notably CFDateCompare and CFNumberCompare. When an array holds Core Foundation objects, you can pass in an appropriate predefined comparator function to the CFArraySortValues function to sort those objects.

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