.TH "Message" 3 "Oct 12, 2003"
.SH Message
.PP
.B
Inherits from:

Object
.PP
.B
Maturity Index:

Experimental
.SH Class Description
.PP
Message instances are used for forwarding Objective-C messages\&.  When an object doesn\&'t respond to a message, the 
.B
doesNotUnderstand:
method is invoked, with an argument that is an instance of this class :
.RS 3

- doesNotUnderstand:msg
.br
{
.br
[msg sentTo:someObject];
.br
return self;
.br
}
.br

.br

.RE
.PP
The user may override 
.B
-doesNotUnderstand:
to send a 
.B
sentTo:
message, which will forward the message to 
.I
someObject
\&.  If 
.I
someObject
doesn\&'t respond to the message, it will receive a 
.B
doesNotUnderstand:
message, and so on\&.
.PP
.B
Note:

To forward class (factory) methods, override the class method 
.B
+doesNotUnderstand:
\&.
.PP
Also see Object\&'s 
.B
doesNotUnderstand:
method for more details\&.
.SH Method types
.PP 
.B
Creating Messages
.RS 3
.br
* selector:dispatch:args:
.RE
.PP 
.B
Querying Messages
.RS 3
.br
* selector
.RE
.PP 
.B
Sending Messages
.RS 3
.br
* sentTo:
.RE
.SH Methods
.PP 
selector:dispatch:args:
.RS 1
+
.B
selector
:(SEL)
.I
s
.B
dispatch
:(ARGIMP)
.I
d
.B
args
:(void *)
.I
a
.RE
.PP
Creates a Message instance with the indicated selector name and pointer to argument structure\&.  The argument structure for a message consists of return value of the method (if not void), followed by the arguments of the method :
.RS 3

struct {
.br
int ret;
.br
int a;
.br
double d;
.br
}
.br

.RE
.PP
The above structure corresponds to a method such as (int)foo:(int)a bar:(double)d\&.
.PP
The 
.I
dispatch
argument is a (compiler generated) function that decodes the arguments from the argument structure, and dispatches the messages\&.
.PP 
selector
.RS 1
- (
SEL
)
.B
selector
.RE
.PP
Returns the selector for this message\&.
.PP 
sentTo:
.RS 1
-
.B
sentTo
:
.I
receiver
.RE
.PP
Forwards the message to 
.I
receiver
(if it\&'s not 
.B
nil
) and returns the message itself (
.I
self
), not the return value of the message that was forwarded to 
.I
receiver
\&.  The latter return value is associated to the Message instance, so that it can be returned to the sender of the message that caused a 
.B
doesNotUnderstand:
message to be sent\&.