"

 COPYRIGHT (c) 1994 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.

"

Message subclass:#MessageSend

	instanceVariableNames:'receiver'

	classVariableNames:''

	poolDictionaries:''

	category:'Kernel-Methods'

!

!MessageSend class methodsFor:'documentation'!

copyright

"

 COPYRIGHT (c) 1994 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 MessageSend can be used for simulation programs.

    They keep some receiver, selector and arguments and can be evaluated

    at any time later. (basically, they are like MessageObjects, but keep

    the receiver in addition to the selector & arguments).

    They can also be used as replacement for simple [self foo]-blocks.

    Of course, they could also be replaced by blocks such as

    '[receiver perform:selector withArguments:arguments]', 

    but blocks are somewhat more expensive in their creation and require

    more storage.

    If you plan to write a simulator and want to queue cillions of blocks,

    try to use MessageSends instead of blocks

    (or even: message, if the receiver is constant);

    this will save you a lot of memory.

    However, the send-operation itself is faster in a block, since it

    will use a better caching scheme (inline-cache) for its send, while

    sending here is done with a #perform:, which is not inline-cached. 

    Also, blocks are more flexible, in that they allow access to local

    variables of the defining method - and work without a need to define an

    extra visited method (read literature on visitor patterns).

    Thus it is not sure, which one is actually better to use ...

    You can either store arguments in the messageSend object, or

    leave them undefined until the send is actually performed, and

    pass any arguments with the value:-messages.

    [See also:]

        Block  Message

    [author:]

        Claus Gittinger

"

!

examples

"

    Example:

       |m|

       m := MessageSend receiver:1 selector:#+ arguments:#(2).

       m value. 

    is almost the same as:

       |m|

       m := [1+2].

       m value. 

    Example2 (a simulation)

        |q|

        q := Queue new.

        ...

        'put some action into the queue'

        q nextPut:(MessageSend receiver:someone selector:#foo arguments:#().

        ...

        'evaluate next action from the queue'

        q next value

        ...

    if all sends are going to the same receiver, use:

        |q|

        q := Queue new.

        ...

        'put some action into the queue'

        q nextPut:(Message selector:#foo arguments:#().

        ...

        'evaluate next action from the queue'

        q next sendTo:someone

        ...

"

! !

!MessageSend class methodsFor:'instance creation'!

receiver:r selector:sel

    "create & return a new instance which can be used to

     send sel to some receiver, r"

    ^ self receiver:r selector:sel arguments:nil

    "

     (MessageSend receiver:nil selector:#foo) value

    "

    "Modified: 20.3.1997 / 21:55:16 / cg"

!

receiver:r selector:sel arguments:argArray

    "create & return a new instance which can be used to

     send sel with arguments to some receiver, r"

    |newMessage|

    newMessage := super new setSelector:sel arguments:argArray.

    newMessage receiver:r.

    ^ newMessage

    "

     (MessageSend receiver:nil selector:#foo: arguments:#(1)) value

    "

    "Modified: 20.3.1997 / 21:55:44 / cg"

! !

!MessageSend methodsFor:'accessing'!

numArgs

    "return the number of arguments of the message"

    ^ selector numArgs

    "Modified: 23.4.1996 / 16:52:51 / cg"

!

receiver

    "return the receiver of the message"

    ^ receiver

    "Modified: 23.4.1996 / 16:52:59 / cg"

!

receiver:r

    "set the receiver of the message"

    receiver := r

    "Modified: 23.4.1996 / 16:53:04 / cg"

! !

!MessageSend methodsFor:'evaluation'!

value

    "evaluate the messagesend with the original arguments"

    ^ receiver perform:selector withArguments:args

!

value:someArgument

    "evaluate the messagesend, with someArgument instead of the original"

    ^ receiver perform:selector with:someArgument

!

value:arg1 value:arg2

    "evaluate the messagesend, with arg1 and arg2 instead of the original

     arguments"

    ^  receiver perform:selector with:arg1 with:arg2

!

value:arg1 value:arg2 value:arg3

    "evaluate the messagesend, with arg1, arg2 and arg3 instead of the original

     arguments"

    ^  receiver perform:selector with:arg1 with:arg2 with:arg3

!

valueWithArguments:argArray

    "evaluate the messagesend, with arguments taken from argArray,

     instead of the original arguments"

    ^  receiver perform:selector withArguments:argArray

! !

!MessageSend methodsFor:'printing & storing'!

displayString

    "return a string for display in inspectors etc."

    ^ 'MessageSend(' , receiver displayString , '>>' , selector , ')'

!

printOn:aStream

    "append a printed representation of the receiver to aStream"

    receiver printOn:aStream.

    aStream nextPutAll:'>>'.

    selector printOn:aStream

    "Modified: 23.4.1996 / 16:53:35 / cg"

! !

!MessageSend class methodsFor:'documentation'!

version

    ^ '$Header: /cvs/stx/stx/libbasic/MessageSend.st,v 1.13 1997-03-20 20:55:56 cg Exp $'

! !