set Specification Sheet

Portable Object Compiler (c) 1997,98. All Rights Reserved.

Set

Inherits from: Cltn

Class Description

Set instances are sets of objects with no duplicate (in the sense of isEqual:) entries. The Dictionary class provides a key-value based interface to sets, and may sometimes be more convenient to use.

To make Sets correctly work, the objects have to implement a pair of comparison methods which must act in a coordinated way :

The message

[newElement isEqual:oldElement]
is expected to report whether newElement is equal to oldElement.

The message

[newElement hash]
should return an integer which is equal for all objects for which isEqual: is true.

Sets place all objects added to them into a hash table based on the results of sending the objects the hash message. Set assumes that, after being added to a set, objects, and their hash value, will not be changed. If any object does change, it will not be located properly in the set. The result of this is that the object will not be found or that it will be added to the set more than once.

Adding Objects

The methods add:, addNTest:, filter:, replace: and add:ifDuplicate: are used to add objects to a set. The difference between these methods is the procedure used in adding, how duplicates are handled and what value is returned.

Method types

Creation

Interrogation

Comparing

Adding

Removing

Testing Contents

Adding and Removing Contents

Combining

Converting

Using Blocks

Making elements perform

Do Blocks

Locating

Printing

Archiving

Methods

new

+new
Returns a new empty set.

new:

+new:(unsigned)n
Returns a new empty set, which can hold at least n elements.

copy

-copy
Returns a new copy of the set.

deepCopy

-deepCopy
Returns a new copy of the set. The elements in the new set are deep copies of the elements in the original set.

emptyYourself

-emptyYourself
Empties all the members of the set (without freeing them). Returns the receiver.

freeContents

-freeContents
Removes and frees all the members of the set, but doesn't free the set itself. Returns the receiver.

free

-free
Frees the set, but not its elements. Returns nil. Do :

set = [[set freeContents] free];
if you want to free the set and its contents.

size

- (unsigned)size
Returns the number of elements in the set.

isEmpty

- (BOOL)isEmpty
Whether the number of objects in the set is equal to zero.

eachElement

-eachElement
Returns a sequence of elements in the set.

seq = [set eachElement];
while ((anElement = [aSeq next])) {
    /* do something */
}
aSeq = [aSeq free];

isEqual:

- (BOOL)isEqual:set
Returns YES if set is a set, if set has the same number of elements as the receiver, and if each member of the contents of set is contained in the receiver's contents.

add:

-add:anObject
Adds anObject if it was not previously in the set, but doesn't inform the caller about the addition because the receiver is always returned.

addNTest:

-addNTest:anObject
Adds anObject if it was not previously in the set. Returns anObject if the addition takes place, otherwise returns nil.

filter:

-filter:anObject
The filter: method has a special purpose. If there is a matching object in the set, then anObject is freed, and the matching object is returned. Otherwise, anObject is added and returned.

add:ifDuplicate:

-add:anObjectifDuplicate:aBlock
Adds and returns anObject, if there was no duplicate previously in the set.

Otherwise, this method evalutes aBlock and returns the matching object (the object that was already in the set).

For example, the filter: method is equivalent to :

[ set add: anObject ifDuplicate: { [anObject free] }];

replace:

-replace:anObject
If a matching object is found, then anObject replaces that object, and the matching object is returned. If there is no matching object, anObject is added to the receiver, and nil is returned.

remove:

-remove:oldObject
Removes oldObject or the element which matches it using isEqual:. Returns the removed entry, or nil if there is no matching entry.

Note: The remove: method of the OrdCltn class is implemented to remove an exact match. The Set class uses a match in the sense of isEqual: instead.

remove:ifAbsent:

-remove:oldObjectifAbsent:exceptionBlock
Removes oldObject or the element which matches it using isEqual:. Returns the removed entry, or return value of exceptionBlock if there is no matching entry.

For example, the method remove: is equivalent to :

[ set remove: oldObject ifAbsent: { nil } ];
Note: The remove: method of the OrdCltn class is implemented to remove an exact match. The Set class uses a match in the sense of isEqual: instead.

find:

-find:anObject
Returns any element in the receiver which isEqual: to anObject. Otherwise, returns nil.

contains:

- (BOOL)contains:anObject
Returns YES if the receiver contains anObject. Otherwise, returns NO. Implementation is in terms of the receiver's find: method (which uses isEqual: and hash to decide whether the object is contained in the set).

includes:

- (BOOL)includes:anObject
This method is equivalent to contains:.

occurrencesOf:

- (unsigned)occurrencesOf:anObject
Returns 1 if anObject is in the receiver, otherwise returns 0. Implementation is in terms of the receiver's find: method (which uses isEqual: and hash).

printOn:

-printOn:(IOD)aFile
Prints a list of the objects in the set by sending each individual object a printOn: message. Returns the receiver.

fileOutOn:

-fileOutOn:aFiler
Writes out non-nil objects in the Set on aFiler. Returns the receiver.

fileInFrom:

-fileInFrom:aFiler
Reads in objects from aFiler. Returns the receiver, which is a set that is not yet usable (until the set gets the awakeFrom: message).

awakeFrom:

-awakeFrom:aFiler
Rehashes the contents of the set, which was previously read from aFiler by the fileInFrom: method. The hash-values of the objects are possibly process or architecture dependent, so they are not stored on the filer. Rather, awakeFrom: recomputes the values.