Class: Message

• Inheritance
• Description
• Related information
• Class protocol
  • instance creation
  • obsolete
  • queries
• Instance protocol
  • Compatibility-Dolphin
  • Compatibility-GNU
  • Compatibility-Squeak
  • accessing
  • printing & storing
  • private-accessing
  • sending

Inheritance:

   Object
   |
   +--Message
      |
      +--MessageSend

Package:

stx:libbasic

Category:

Kernel-Methods

Version:

rev: 1.33 date: 2007/05/31 15:51:35

user: cg

file: Message.st directory: libbasic

module: stx stc-classLibrary: libbasic

Author:

Claus Gittinger

Description:

Instances of Message represent a message being sent.
During normal execution, message objects are NEVER used -
instead, argument passing is done more performant via the stack
or in registers (depends on how your C compiler passes arguments).

However, messageObjects ARE created, when a message send fails 
(i.e. some message is not understood).
In this case, the selector and arguments of the failing messare
are squashed into a new instance of Message, and a #doesNotUnderstand: 
message is sent to the original receiver, passing the message object
as argument.

Typically, #doesNotUnderstand: is not redefined in the receivers class,
therefore Object>>doesNotUnderstand: gets evaluated.
There, a debugger is opened and the thread is suspended.
However, it is possible to redefine this method, which
allows for re-evaluation of the failed send (after some cleanup),
to upload some code or to simply ignore the error.

As an example of its use, see the implementation of the Autoload-class,
or how ScrollableView forwards unknown messages to its slave-view.

Elegance hint: actually, Object>>doesNotUnderstand: raises an exception
which can be handled - in most situations, providing an exception handler 
instead of redefining #doesNotUnderstand is the better way to do things.


Notice:
Since the layout of Message-objects is known by the runtime system
(it has to create those objects in case of a failure)
it is not allowed to change the definition of this class.

Related information:

    Signal
    Exception
    MessageSend

Class protocol:

 selector: aSymbol

return a new message object for a send without arguments

 selector: aSymbol argument: anArg

return a new message object for a send with one argument

 selector: aSymbol argument: arg1 argument: arg2

return a new message object for a send with two arguments

 selector: aSymbol arguments: argArray

return a new message object for a send with many arguments

 selector: aSymbol with: anArg

return a new message object for a send with one argument.
OBSOLETE: use #selector:argument: for ST-80 compatibility.

** This is an obsolete interface - do not use it (it may vanish in future versions) **

 selector: aSymbol with: arg1 with: arg2

return a new message object for a send with two arguments.
OBSOLETE: use #selector:arguments: for ST-80 compatibility.

** This is an obsolete interface - do not use it (it may vanish in future versions) **

 selector: aSymbol withAll: argArray

return a new message object for a send with many arguments.
OBSOLETE: use #selector:arguments: for ST-80 compatibilty.

** This is an obsolete interface - do not use it (it may vanish in future versions) **

 isBuiltInClass

return true if this class is known by the run-time-system.
Here, true is returned for myself, false for subclasses.

Instance protocol:

 value: aReceiver

evaluate myself for receiver.
Same as #sendTo: - compatibility with Dolphin

 reinvokeFor: aReceiver

send the selector with argument to a receiver.
Same as sendTo: - for GNU-ST compatibility.

 argument

return the 1st argument of the message

 arg1

return the first argument of the message

 argumentCount

VisualAge/ANSI compatibility: return the number of arguments of the message

 arguments

return the arguments of the message

 arguments: argArray

set arguments of the receiver

 numArgs

return the number of arguments of the message

 selector

return the selector of the message

 selector: aSymbol

 displayString

return a string for display in inspectors etc.

 printOn: aStream

append a user printed representation of the receiver to aStream.
The format is suitable for a human - not meant to be read back.

 setSelector: aSymbol

 setSelector: aSymbol arguments: argArray

set selector and arguments of the receiver

 sendTo: aReceiver

send the selector with argument to aReceiver