Copyright ã1994 by NeXT Computer, Inc.  All Rights Reserved.

Foundation Kit Functions

Memory Allocation Functions

Get the Virtual Memory Page Size

unsigned NSPageSize(void)	Returns the number of bytes in a page.

unsigned NSLogPageSize(void)	Returns the binary log of the page size.

unsigned NSRoundDownToMultipleOfPageSize(unsigned byteCount)
	Returns the multiple of the page size that is closest to, but not greater than, byteCount.

unsigned NSRoundUpToMultipleOfPageSize(unsigned byteCount)
	Returns the multiple of the page size that is closest to, but not less than, byteCount.

Get the Amount of Real Memory

unsigned NSRealMemoryAvailable(void)	Returns the number of bytes available in the RAM hardware.

Allocate or Free Virtual Memory

void *NSAllocateMemoryPages(unsigned byteCount)
	Allocates the integral number of pages whose total size is closest to, but not less than, byteCount, with the pages guaranteed to be zero-filled.

void NSDeallocateMemoryPages(void *pointer, 	Deallocates memory that was allocated with
unsigned byteCount)	 	NSAllocateMemoryPages().

void NSCopyMemoryPages(const void *source, 	Copies (or copies-on-write) byteCount bytes from source
void *destination, 		to destination.
unsigned byteCount)

Get a Zone

NSZone *NSCreateZone(unsigned startSize, 	Creates and returns a pointer to a new zone of startSize
unsigned granularity, 		bytes, which will grow and shrink by granularity bytes.
BOOL canFree)		If canFree is NO, the allocator will never free memory, and malloc() will be fast.

NSZone *NSDefaultMallocZone(void)	Returns the default zone, which is created automatically at startup. This is the zone used by the standard C function malloc().

NSZone *NSZoneFromPointer(void *pointer)	Returns the zone for the pointer block of memory, or NULL if the block was not allocated from a zone. The pointer must be one that was returned by a prior call to an allocation function.

Allocate or Free Memory in a Zone

void *NSZoneMalloc(NSZone *zone, 	Allocates size bytes in zone, and returns a pointer to the
unsigned size)		allocated memory.

void *NSZoneCalloc(NSZone *zone, 	Allocates enough memory from zone for numElems
unsigned numElems, 		elements, each with a size of numBytes bytes, and
unsigned numBytes)		returns a pointer to the allocated memory. The memory is initialized with zeros.

void *NSZoneRealloc(NSZone *zone, 	Changes the size of the block of memory pointed to by
void *pointer, 		pointer to size bytes. It may allocate new memory to
unsigned size)		replace the old, in which case it moves the contents of the old memory block to the new block, up to a maximum of size bytes. The pointer may be NULL.

void NSRecycleZone(NSZone *zone)	Frees zone after adding any of its pointers still in use to the default zone. (This strategy prevents retained objects from being inadvertently destroyed.)

void NSZoneFree(NSZone *zone, 	Returns memory to the zone from which it was allocated. 
void *pointer)	The standard C function free() does the same, but spends time finding which zone the memory belongs to.

Name a Zone

void NSSetZoneName(NSZone *zone, 	Sets the specified zone's name to name, which can aid in
NSString *name)		debugging.

NSString *NSZoneName(NSZone *zone)	Returns the name of zone.

Object Allocation Functions

Allocate or Free an Object

NSObject *NSAllocateObject(Class aClass, 	Allocates and returns a pointer to an instance of aClass,
unsigned extraBytes, 		created in the specified zone (or in the default zone, if
NSZone *zone)		zone is NULL). The extraBytes argument (usually zero) states the number of extra bytes required for indexed instance variables.

NSObject *NSCopyObject(NSObject *anObject, 	Creates and returns a new object that's an exact copy of
unsigned extraBytes, 		anObject. The second and third arguments have the
NSZone *zone)		same meaning as in NSAllocateObject().

void NSDeallocateObject(NSObject *anObject)	Deallocates anObject, which must have been allocated using NSAllocateObject().

Decide Whether to Retain an Object

BOOL NSShouldRetainWithZone(NSObject *anObject, 
NSZone *requestedZone)	Returns YES if requestedZone is NULL, the default zone, or the zone in which anObject was allocated. This function is typically called from inside an NSObject's copyWithZone: method, when deciding whether to retain anObject as opposed to making a copy of it.

Modify the Number of References to an Object

BOOL NSDecrementExtraRefCountWasZero(id anObject)
	Returns YES if the externally maintained ªextra reference countº for anObject is zero; otherwise, this function decrements the count and returns NO.

void NSIncrementExtraRefCount(id anObject)	Increments the externally maintained ªextra reference countº for anObject. The first reference (typically done in the +alloc method) isn't maintained externally, so there's no need to call this function for that first reference.

Error-Handling Functions

Change the Top-level Error Handler

NSUncaughtExceptionHandler *NSGetUncaughtExceptionHandler(void)
	Returns a pointer to the function serving as the top-level error handler. This handler will process exceptions raised outside of any exception-handling domain.

void NSSetUncaughtExceptionHandler(NSUncaughtExceptionHandler *handler)
	Sets the top-level error-handling function to handler. If handler is NULL or this function is never invoked, the default top-level handler is used.

Macros to Handle an Exception

NS_DURING	Marks the beginning of an exception-handling domain (a portion of code delimited by NS_DURING and NS_HANDLER). When an error is raised anywhere within the exception-handling domain, program execution jumps to the first line of code in the exception handler. It's illegal to exit the exception-handling domain by any other means than NS_VALUERETURN, NS_VOIDRETURN, or falling out the bottom.

NS_ENDHANDLER	Marks the ending of an exception handler (a portion of code delimited by NS_HANDLER and NS_ENDHANDLER).

NS_HANDLER	Marks the ending of an exception-handling domain and the beginning of the corresponding exception handler. Within the scope of the handler, a local variable called exception stores the raised exception. Code delimited by NS_HANDLER and NS_ENDHANDLER is never executed except when an error is raised in the preceding exception-handling domain.

value NS_VALUERETURN(value, type) 	Causes the method (or function) in which this macro occurs to immediately return value of type type. This macro can only be placed within an exception-handling domain.

NS_VOIDRETURN	Causes the method (or function) in which this macro occurs to return immediately, with no return value. This macro can only be placed within an exception-handling domain.

Call the Assertion Handler from the Body of an Objective-C Method

NSAssert(BOOL condition, 	Calls the NSAssertionHandler object for the current thread 
NSString *description) 		if condition is false. The description should explain the error, formatted as for the standard C function printf(); it need not include the object's class and method name, since they're passed automatically to the handler.

NSAssert1(BOOL condition, 	Like NSAssert(), but the format string description
NSString *description, 		includes a conversion specification (such as %s or %d)
arg)		for the argument arg, in the style of printf(). You can pass an object in arg by specifying %@, which gets replaced by the string that the object's description method returns.

NSAssert2(BOOL condition, 	Like NSAssert1(), but with two arguments.
NSString *description, 
arg1, 
arg2) 

NSAssert3(BOOL condition, 	Like NSAssert1(), but with three arguments.
NSString *description, 
arg1, 
arg2, 
arg3)	

NSAssert4(BOOL condition, 	Like NSAssert1(), but with four arguments.
NSString *description, 
arg1, 
arg2, 
arg3,
 arg4) 	

NSAssert5(BOOL condition, 	Like NSAssert1(), but with five arguments.
NSString *description, 
arg1, 
arg2, 
arg3, 
arg4, 
arg5) 

Call the Assertion Handler from the Body of a C Function

NSCAssert(BOOL condition, 	Calls the NSAssertionHandler object for the current thread 
NSString *description) 		if condition is false. The description should explain the error, formatted as for the standard C function printf(); it need not include the function name, which is passed automatically to the handler.

NSCAssert1(BOOL condition, 	Like NSCAssert(), but the format string description
NSString *description, 		includes a conversion specification (such as %s or %d)
arg) 		for the argument arg, in the style of printf().

NSCAssert2(BOOL condition, 	Like NSCAssert1(), but with two arguments.
NSString *description, 
arg1, 
arg2) 

NSCAssert3(BOOL condition, 	Like NSCAssert1(), but with three arguments.
NSString *description, 
arg1, 
arg2, 
arg3) 

NSCAssert4(BOOL condition, 	Like NSCAssert1(), but with four arguments.
NSString *description, 
arg1, 
arg2, 
arg3, 
arg4) 

NSCAssert5(BOOL condition, 	Like NSCAssert1(), but with five arguments.
NSString *description, 
arg1, 
arg2, 
arg3, 
arg4, 
arg5) 

Validate a Parameter

NSParameterAssert(BOOL condition) 	Like NSAssert(), but the description passed to the assertion handler is ªInvalid parameter not satisfying: º followed by the text of condition (which can be any boolean expression).

NSCParameterAssert(BOOL condition) 	Like NSParameterAssert(), but to be called from the body of a C function.

Geometric Functions

Create Basic Structures

NSPoint NSMakePoint(float x, float y)	Create an NSPoint having the coordinates x and y.

NSSize NSMakeSize(float w, float h)	Create an NSSize having the specified width and height.

NSRect NSMakeRect(float x, float y, float w, float h)  Create an NSRect having the specified origin and size.

NSRange NSMakeRange(unsigned int location, unsigned int length)
	Create an NSRange having the specified location and length.

Get a Rectangle's Coordinates

float NSMaxX(NSRect aRect)	Returns the largest x-coordinate value within aRect.

float NSMaxY(NSRect aRect)	Returns the largest y-coordinate value within aRect.

float NSMidX(NSRect aRect)	Returns the x-coordinate of the rectangle's center point.

float NSMidY(NSRect aRect)	Returns the y-coordinate of the rectangle's center point.

float NSMinX(NSRect aRect)	Returns the smallest x-coordinate value within aRect.

float NSMinY(NSRect aRect)	Returns the smallest y-coordinate value withinaRect .

float NSWidth(NSRect aRect)	Returns the width of aRect.

float NSHeight(NSRect aRect)	Returns the height of aRect.

Modify a Copy of a Rectangle

NSRect NSInsetRect(NSRect aRect, 	Returns a copy of the rectangle aRect, altered by moving
float dX, 		the two sides that are parallel to the y-axis inwards by
float dY)		dX, and the two sides parallel to the x-axis inwards by dY.

NSRect NSOffsetRect(NSRect aRect, 	Returns a copy of the rectangle aRect, with its location
float dX, 		shifted by dX along the x-axis and by dY along the
float dY)		y-axis.

void NSDivideRect(NSRect inRect, 	Creates two rectangles, slice and remainder, from inRect,
NSRect *slice, 		by dividing inRect with a line that's parallel to one of
NSRect *remainder, 		inRect's sides (namely, the side specified by edgeÐ
float amount, 		either NSMinXEdge, NSMinYEdge, NSMaxXEdge, or
NSRectEdge edge)		NSMaxYEdge). The size of slice is determined by amount, which measures the distance from edge.

NSRect NSIntegralRect(NSRect aRect)	Returns a copy of the rectangle aRect, expanded outwards just enough to ensure that none of its four defining values (x, y, width, and height) have fractional parts. If aRect's width or height is zero or negative, this function returns a rectangle with origin at (0.0, 0.0) and with zero width and height.

Compute a Third Rectangle from Two Rectangles

NSRect NSUnionRect(NSRect aRect, 	 Returns the smallest rectangle that completely encloses
NSRect bRect)	 	both aRect and bRect. If one of the rectangles has zero (or negative) width or height, a copy of the other rectangle is returned; but if both have zero (or negative) width or height, the returned rectangle has its origin at (0.0, 0.0) and has zero width and height.

NSRect NSIntersectionRect(NSRect aRect, 	Returns the graphic intersection of aRect and bRect. If the
NSRect bRect)		two rectangles don't overlap, the returned rectangle has its origin at (0.0, 0.0) and zero width and height. (This includes situations where the intersection is a point or a line segment.)

Test Geometric Relationships

BOOL NSEqualRects(NSRect aRect, 	Returns YES if the two rectangles aRect and bRect are
NSRect bRect)		identical, and NO otherwise.

BOOL NSEqualSizes(NSSize aSize, 	Returns YES if the two sizes aSize and bSize are identical,
NSSize bSize)		and NO otherwise.

BOOL NSEqualPoints(NSPoint aPoint, 	Returns YES if the two points aPoint and bPoint are
NSPoint bPoint)		identical, and NO otherwise.

BOOL NSIsEmptyRect(NSRect aRect)	Returns YES if the rectangle encloses no area at allÐthat is, if its width or height is zero or negative.

BOOL NSMouseInRect(NSPoint aPoint, 	Returns YES if the point represented by aPoint is located
NSRect aRect, 		within the rectangle represented by aRect. It assumes
BOOL flipped)		an unscaled and unrotated coordinate system; the argument flipped should be YES if the coordinate system has been flipped so that the positive y-axis extends downward. This function is used to determine whether the hot spot of the cursor lies inside a given rectangle.

BOOL NSPointInRect(NSPoint aPoint, 	Performs the same test as NSMouseInRect(), but assumes
NSRect aRect)		a flipped coordinate system.

BOOL NSContainsRect(NSRect aRect, 	Returns YES if aRect completely encloses bRect. For this
NSRect bRect)		to be true, bRect can't be empty and none of its sides can touch any of aRect's.

Get a String Representation

NSString *NSStringFromPoint(NSPoint aPoint)	Returns a string of the form ª{x=a; y=b}º, where a and b are the x- and y-coordinates of aPoint.

NSString *NSStringFromRect(NSRect aRect)	Returns a string of the form ª{x=a; y=b; width=c; height=d}º, where a, b, c, and d are the x- and y-coordinates and the width and height, respectively, of aRect.

NSString *NSStringFromSize(NSSize aSize)	Returns a string of the form ª{width=a; height=b}º, where a and b are the width and height of aSize.

Range Functions

Query a Range

BOOL NSEqualRanges(NSRange range1, 	Returns YES if range1 and range2 have the same
NSRange range2)		locations and lengths.

unsigned NSMaxRange(NSRange range)	Returns range.location + range.lengthÐin other words, the number one greater than the maximum value within the range. 

BOOL NSLocationInRange(unsigned location, 	Returns YES if location is in range (that is, if location is
NSRange range)		greater than or equal to range.location and location is less than NSMaxRange(range)).

 Compute a Range from Two Other Ranges

NSRange NSUnionRange(NSRange range1, 	Returns a range whose maximum value is the greater of
NSRange range2)		range1's and range2's maximum values, and whose location is the lesser of the two range's locations.

NSRange NSIntersectionRange(NSRange range1, 	Returns a range whose maximum value is the lesser of
NSRange range2)		range1's and range2's maximum values, and whose location is the greater of the two range's locations. However, if the two ranges don't intersect, the returned range has a location and length of zero.

Get a String Representation

NSString *NSStringFromRange(NSRange range)	Returns a string of the form: ª{location = a; length = b}º, where a and b are non-negative integers.

Hash Table Functions

Create a Table

NSHashTable *NSCreateHashTable(NSHashTableCallBacks callBacks, 
unsigned capacity)	Creates, and returns a pointer to, an NSHashTable in the default zone; the table's size is dependent on (but generally not equal to) capacity. If capacity is 0, a small hash table is created. The NSHashTableCallBacks structure callBacks has five pointers to functions (documented under ªTypes and Constantsº), with the following defaults: pointer hashing, if hash() is NULL; pointer equality, if isEqual() is NULL; no call-back upon adding an element, if retain() is NULL; no call-back upon removing an element, if release() is NULL; and a function returning a pointer's hexadecimal value as a string, if describe() is NULL. The hashing function must be defined such that if two data elements are equal, as defined by the comparison function, the values produced by hashing on these elements must also be equal. Also, data elements must remain invariant if the value of the hashing function depends on them; for example, if the hashing function operates directly on the characters of a string, that string can't change.

NSHashTable *NSCreateHashTableWithZone(NSHashTableCallBacks callBacks, 
unsigned capacity, 	Like NSCreateHashTable(), but creates the hash table in
NSZone *zone)		zone instead of in the default zone. (If zone is NULL, the default zone is used.)

NSHashTable *NSCopyHashTableWithZone(NSHashTable *table, 
NSZone *zone)	Returns a pointer to a new copy of table, created in zone and containing copies of table's pointers to data elements. If zone is NULL, the default zone is used.

Free a Table

void NSFreeHashTable(NSHashTable *table)	Releases each element of the specified hash table and frees the table itself. 

void NSResetHashTable(NSHashTable *table)	 Releases each element but doesn't deallocate the table. This is useful for preserving the table's capacity. 

Compare Two Tables

BOOL NSCompareHashTables(NSHashTable *table1, 
NSHashTable *table2)	Returns YES if the two hash tables are equalÐthat is, if each element of table1 is in table2, and the two tables are the same size.

Get the Number of Items

unsigned NSCountHashTable(NSHashTable *table)
	Returns the number of elements in table.

Retrieve Items

void *NSHashGet(NSHashTable *table, 	Returns the pointer in the table that matches pointer (as
const void *pointer)		defined by the isEqual() call-back function). If there is no matching element, the function returns NULL

NSArray *NSAllHashTableObjects(NSHashTable *table)
	Returns an array object containing all the elements of table. This function should be called only when the table elements are objects, not when they're any other data type.

NSHashEnumerator NSEnumerateHashTable(NSHashTable *table)
	Returns an NSHashEnumerator structure that will cause successive elements of table to be returned each time this enumerator is passed to NSNextHashEnumeratorItem().

void *NSNextHashEnumeratorItem(NSHashEnumerator *enumerator)
	Returns the next element in the table that enumerator is associated with, or NULL if enumerator has already iterated over all the elements.

Add or Remove an Item

void NSHashInsert(NSHashTable *table, 	Inserts pointer, which must not be NULL, into table. If 
const void *pointer)		pointer matches an item already in the table, the previous pointer is released using the release() call-back function that was specified when the table was created.

void NSHashInsertKnownAbsent(NSHashTable *table, 
const void *pointer)	Inserts pointer, which must not be NULL, into table. Unike NSHashInsert(), this function raises NSInvalidArgumentException if table already includes an element that matches pointer.

void *NSHashInsertIfAbsent(NSHashTable *table,	If pointer matches an item already in table, this function
const void *pointer)	 	returns the pre-existing pointer; otherwise, it adds pointer to the table and returns NULL.

void NSHashRemove(NSHashTable *table, 	If pointer matches an item already in table, this function
const void *pointer)		 releases the pre-existing item.

Get a String Representation

NSString *NSStringFromHashTable(NSHashTable *table)
	Returns a string describing the hash table's contents. The function iterates over the table's elements, and for each one appends the string returned by the describe() call-back function. If NULL was specified for the call-back function, the hexadecimal value of each pointer is added to the string.

Map Table Functions

Create a Table

NSMapTable *NSCreateMapTable(NSMapTableKeyCallBacks keyCallBacks, 
NSMapTableValueCallBacks valueCallBacks, 
unsigned capacity)	Creates, and returns a pointer to, an NSMapTable in the default zone; the table's size is dependent on (but generally not equal to) capacity. If capacity is 0, a small map table is created. The NSMapTableKeyCallBacks arguments are structures (documented under ªTypes and Constantsº) that are very similar to the call-back structure used by NSCreateHashTable(); in fact, they have the same defaults as documented for that function.

NSMapTable *NSCreateMapTableWithZone(NSMapTableKeyCallBacks keyCallBacks, 
NSMapTableValueCallBacks valueCallBacks, 
unsigned capacity, 	Like NSCreateMapTable(), but creates the map table in
NSZone *zone)		zone instead of in the default zone. (If zone is NULL, the default zone is used.)

NSMapTable *NSCopyMapTableWithZone(NSMapTable *table, 
NSZone *zone)	Returns a pointer to a new copy of table, created in zone and containing copies of table's key and value pointers. If zone is NULL, the default zone is used.

Free a Table

void NSFreeMapTable(NSMapTable *table)	Releases each key and value of the specified map table and frees the table itself.

void NSResetMapTable(NSMapTable *table)	Releases each key and value but doesn't deallocate the table. This is useful for preserving the table's capacity.

Compare Two Tables:

BOOL NSCompareMapTables(NSMapTable *table1, 
NSMapTable *table2)	Returns YES if each key of table1 is in table2, and the two tables are the same size. Note that this function does not compare values, only keys.

Get the Number of Items

unsigned NSCountMapTable(NSMapTable *table)	Returns the number of key/value pairs in table.

Retrieve Items

BOOL NSMapMember(NSMapTable *table, 	Returns YES if table contains a key equal to key. If so,
const void *key, 		originalKey is set to key, and value is set to the value that
void **originalKey, 		the table maps to key.
void **value)

void *NSMapGet(NSMapTable *table, 	Returns the value that table maps to key, or NULL if the
const void *key)		table doesn't contain key.

NSMapEnumerator NSEnumerateMapTable(NSMapTable *table)
	Returns an NSMapEnumerator structure that will cause successive key/value pairs of table to be visited each time this enumerator is passed to NSNextMapEnumeratorPair().

BOOL NSNextMapEnumeratorPair(NSMapEnumerator *enumerator, 
void **key, 	Returns NO if enumerator has already iterated over all the
void **value)		elements in the table that enumerator is associated with. Otherwise, this function sets key and value to match the next key/value pair in the table, and returns YES. 

NSArray *NSAllMapTableKeys(NSMapTable *table)
	Returns an array object containing all the keys in table. This function should be called only when the table keys are objects, not when they're any other type of pointer.

NSArray *NSAllMapTableValues(NSMapTable *table)
	Returns an array object containing all the values in table. This function should be called only when the table values are objects, not when they're any other type of pointer.

Add or Remove an Item

void NSMapInsert(NSMapTable *table, 	Inserts key and value into table. If key matches a key
const void *key, 		already in the table, value is retained and the previous
const void *value)		value is released, using the retain and release call-back functions that were specified when the table was created. Raises NSInvalidArgumentException if key is equal to the notAKeyMarker field of the table's NSMapTableKeyCallBacks structure.

void *NSMapInsertIfAbsent(NSMapTable *table, 	If key matches a key already in table, this function returns
const void *key, 		the pre-existing key; otherwise, it adds key and value to
const void *value)		the table and returns NULL. Raises NSInvalidArgumentException if key is equal to the notAKeyMarker field of the table's NSMapTableKeyCallBacks structure.

void NSMapInsertKnownAbsent(NSMapTable *table, 
const void *key, 	Inserts key (which must not be notAKeyMarker) and
const void *value)		value into table. Unike NSMapInsert(), this function raises NSInvalidArgumentException if table already includes a key that matches key.

void NSMapRemove(NSMapTable *table, 	If key matches a key already in table, this function releases
const void *key)		the pre-existing key and its corresponding value.

NSString *NSStringFromMapTable(NSMapTable *table)
	Returns a string describing the map table's contents. The function iterates over the table's key/value pairs, and for each one appends the string ªa = b;\nº, where a and b are the key and value strings returned by the corresponding describe() call-back functions. If NULL was specified for the call-back function, a and b are the key and value pointers, expressed as hexadecimal numbers.

Miscellaneous Functions

Get Information about a User

NSString *NSUserName(void)

NSString *NSHomeDirectory(void)

NSString *NSHomeDirectoryForUser(NSString * userName)

Log an Error Message

void NSLog(NSString *format, ...)	Writes to stderr an error message of the form: 
ªtime processName processID formatº. The format argument to NSLog() is a format string in the style of the standard C function printf(), followed by an arbitrary number of arguments that match conversion specifications (such as %s or %d) in the format string. (You can pass an object in the list of arguments by specifying %@ in the format stringÐthis conversion specification gets replaced by the string that the object's description method returns.)

void NSLogv(NSString *format, va_list args)	Like NSLog(), but the arguments to the format string are passed in a single va_list, in the manner of vprintf(). 

Get Localized Versions of Strings

NSString *NSLocalizedString(NSString *key,	Returns a localized version of the string designated by key.
NSString *comment)		The default string table (Localizable.strings) in the main bundle is searched for key. comment is ignored, but can provide information for translators.

NSString *NSLocalizedStringFromTable(NSString *key,
NSString *tableName, 	Like NSLocalizedString(), but searches the specified 
NSString *comment)		table.

NSString *NSLocalizedStringFromTableInBundle(NSString *key,
NSString *tableName, 	Like NSLocalizedStringFromTable, but uses the 
NSBundle *aBundle, 		specified bundle instead of the application's main 
NSString *comment)		bundle.

Convert to and from a String

Class NSClassFromString(NSString *aClassName)	
	Returns the class object named by aClassName, or nil if none by this name is currently loaded.

SEL NSSelectorFromString(NSString *aSelectorName)
	Returns the selector named by aSelectorName, or zero if none by this name exists.

NSString *NSStringFromClass(Class aClass)	Returns an NSString containing the name of aClass.

NSString *NSStringFromSelector(SEL aSelector)	Returns an NSString containing the name of aSelector.

Compose a Message To Be Sent Later to an Object

NSInvocation *NS_INVOCATION(Class aClass, 	Returns an NSInvocation object which you can later ask to
 instanceMessage)	 	dispatch instanceMessage to an instance of aClass. (You later use NSInvocation's setTarget: method to make a specific instance of aClass the receiver of the message, after which you use invoke to cause the message to be sent and getReturnValue: to retrieve the result.) Because this is a macro, message can be any Objective C message understood by an instance of aClass, even a message with multiple arguments.

NSInvocation *NS_MESSAGE(id anObject, 	Like NS_INVOCATION(), but the first argument is an
 instanceMessage)		 instance of a class, rather than a class. The target of the message will be anObject, so later you don't use setTarget:, only invoke and getReturnValue:.