"
 COPYRIGHT (c) 1988 by Claus Gittinger
	      All Rights Reserved

 This software is furnished under a license and may be used
 only in accordance with the terms of that license and with the
 inclusion of the above copyright notice.   This software may not
 be provided or otherwise made available to, or used by, any
 other person.  No title to or ownership of the software is
 hereby transferred.
"

Object subclass:#Message
	instanceVariableNames:'selector args'
	classVariableNames:''
	poolDictionaries:''
	category:'Kernel-Methods'
!

!Message class methodsFor:'documentation'!

copyright
"
 COPYRIGHT (c) 1988 by Claus Gittinger
	      All Rights Reserved

 This software is furnished under a license and may be used
 only in accordance with the terms of that license and with the
 inclusion of the above copyright notice.   This software may not
 be provided or otherwise made available to, or used by, any
 other person.  No title to or ownership of the software is
 hereby transferred.
"
!

documentation
"
    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.

    [See also:]
        Signal  Exception  MessageSend

    [author:]
        Claus Gittinger
"
! !

!Message class methodsFor:'instance creation'!

selector:aSymbol
    "return a new message object for a send without arguments"

    ^ self basicNew setSelector:aSymbol arguments:nil
!

selector:aSymbol argument:anArg
    "return a new message object for a send with one argument"

    ^ self basicNew setSelector:aSymbol arguments:(Array with:anArg)
!

selector:aSymbol arguments:argArray
    "return a new message object for a send with many arguments"

    ^ self basicNew setSelector:aSymbol arguments:argArray
!

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

    ^ self basicNew setSelector:aSymbol arguments:(Array with:anArg)
!

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."

    ^ self basicNew setSelector:aSymbol arguments:(Array with:arg1 with:arg2)
!

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

    ^ self basicNew setSelector:aSymbol arguments:argArray
! !

!Message class methodsFor:'queries'!

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

    ^ self == Message

    "Modified: 23.4.1996 / 15:59:30 / cg"
! !

!Message methodsFor:'accessing'!

arguments
    "return the arguments of the message"

    ^ args
!

selector
    "return the selector of the message"

    ^ selector
! !

!Message methodsFor:'printing & storing'!

displayString
    "return a string for display in inspectors etc."

    ^ 'Message(' , selector , ')'
!

printOn:aStream
    "return a string for printing the receiver"

    selector printOn:aStream
! !

!Message methodsFor:'private accessing'!

setSelector:aSymbol arguments:argArray
    "set selector and arguments of the receiver"

    selector := aSymbol.
    args := argArray
! !

!Message methodsFor:'sending'!

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

    ^ self sendTo:aReceiver
!

sendTo:aReceiver
    "send the selector with argument to some receiver"

    ^ aReceiver perform:selector withArguments:args
! !

!Message class methodsFor:'documentation'!

version
    ^ '$Header: /cvs/stx/stx/libbasic/Message.st,v 1.19 1996-04-25 16:48:48 cg Exp $'
! !