Block(3) UNIX System V (Apr 20, 1999) Block(3)
Block
Inherits from:
Object
Maturity Index:
Experimental
Class Description
Objective-C Blocks are similar to block expressions in
Smalltalk. Blocks are a way to express deferred
computations; computations to be written at one place but
invoked from another.
The Portable Object Compiler uses blocks for error handling
i.e., the processing of exceptional conditions that
interrupt the normal flow of program execution, such as out
of memory, division by zero etc.
The Object method error: and the Block instance method
ifError: are used for this.
Blocks are a non-standard part of the Objective-C language;
this implementation, the first and most powerful as far as
we know, is based on Brad Cox's TaskMaster paper where the
same concept is discussed under the name of Action
Expressions.
For a discussion on what Blocks are, and how to use them, we
refer to the document Objective-C Blocks .
The compiler has an option -noBlocks that can be used to
turn off the special syntax for Blocks.
Method types
Exception Handling
* errorHandler
* errorHandler:
* ifError:
* value:ifError:
Evaluating Blocks
* value
* intvalue
* atExit
* value:
* intvalue:
* value:value:
* intvalue:value:
Control Flow
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Block(3) UNIX System V (Apr 20, 1999) Block(3)
* repeatTimes:
Methods
errorHandler
+ errorHandler
Returns the default handler, as set by errorHandler: , or,
if none was explicitely set, it uses the following handler:
id errorHandler = { :msg :rcv | fprintf(stderr,[msg
str]);abort(); };
errorHandler:
+ errorHandler : aHandler
Make aHandler the default error handler. Returns the
handler that was previously registered as default handler.
ifError:
- ifError : aHandler
Evaluates the receiver of the message and returns its return
value. If an exception is raised, evaluates aHandler .
This works by pushing aHandler on a stack of error handlers,
the method halt: temporarily pops off an error handler and
evaluates it with a message and receiver object as arguments
:
[ { ... } ifError: { :msg :rcv | ... }];
Note:
It is an error to have a non-local return from within the
receiver, as this would leave an error handler dangling. It
is allowed to return however, from within the error handler.
value:ifError:
- value : anObject ifError : aHandler
Like ifError: but the receiving block can take an argument.
value
- value
Evaluates the receiver of the message and returns its return
value.
intvalue
- ( int ) intvalue
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Block(3) UNIX System V (Apr 20, 1999) Block(3)
Evaluates the receiver of the message and returns its return
value.
atExit
- atExit
Evaluates the receiver of the message when the process
exits. See the ANSI C function atexit() for more details.
There's a maximum of 32 exit Blocks that can be registered
to be automatically called on exit. Blocks are evaluated in
reverse order of their registration.
value:
- value : anObject
Evaluates, with anObject as argument, the receiver of the
message and returns its return value.
intvalue:
- ( int ) intvalue : anObject
Evaluates, with anObject as argument, the receiver of the
message and returns its return value.
value:value:
- value : firstObject value : secondObject
Evaluates the receiver of the message with two arguments and
returns its return value.
intvalue:value:
- ( int ) intvalue : firstObject value : secondObject
Evaluates the receiver of the message with two arguments and
returns its return value.
repeatTimes:
- repeatTimes :(int) n
Method to evaluate the receiver Block n times. Similar to
the Smalltalk method timesRepeat: but with argument and
receiver interchanged. Returns self.
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