'\"
'\" Copyright (c) 2007 Donal K. Fellows
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
.TH class n 0.1 TclOO "TclOO Commands"
.so man.macros
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
oo::class \- class of all classes
.SH SYNOPSIS
.nf
package require TclOO

\fBoo::class\fI method \fR?\fIarg ...\fR?
.fi
.SH "CLASS HIERARCHY"
.nf
\fBoo::object\fR
   \(-> \fBoo::class\fR
.fi
.BE
.SH DESCRIPTION
.PP
Classes are objects that can manufacture other objects according to a pattern
stored in the factory object (the class). An instance of the class is created
by calling one of the class's factory methods, typically either \fBcreate\fR
if an explicit name is being given, or \fBnew\fR if an arbitrary unique name
is to be automatically selected.
.PP
The \fBoo::class\fR class is the class of all classes; every class is an
instance of this class, which is consequently an instance of itself. This
class is a subclass of \fBoo::object\fR, so every class is also an object.
Additional metaclasses (i.e., classes of classes) can be defined if necessary
by subclassing \fBoo::class\fR. Note that the \fBoo::class\fR object hides the
\fBnew\fR method on itself, so new classes should always be made using the
\fBcreate\fR method.
.SS CONSTRUCTOR
.PP
The constructor of the \fBoo::class\fR class takes an optional argument which,
if present, is sent to the \fBoo::define\fR command (along with the name of
the newly-created class) to allow the class to be conveniently configured at
creation time.
.SS DESTRUCTOR
The \fBoo::class\fR class does not define an explicit destructor. However,
when a class is destroyed, all its subclasses and instances are also
destroyed, along with all objects that it has been mixed into.
.SS "EXPORTED METHODS"
.TP
\fIcls \fBcreate \fIname \fR?\fIarg ...\fR?
.
This creates a new instance of the class \fIcls\fR called \fIname\fR (which is
resolved within the calling context's namespace if not fully qualified),
passing the arguments, \fIarg ...\fR, to the constructor, and (if that returns
a successful result) returning the fully qualified name of the created object
(the result of the constructor is ignored). If the constructor fails (i.e.
returns a non-OK result) then the object is destroyed and the error message is
the result of this method call.
.TP
\fIcls \fBnew \fR?\fIarg ...\fR?
.
This creates a new instance of the class \fIcls\fR with a new unique name,
passing the arguments, \fIarg ...\fR, to the constructor, and (if that returns
a successful result) returning the fully qualified name of the created object
(the result of the constructor is ignored). If the constructor fails (i.e.,
returns a non-OK result) then the object is destroyed and the error message is
the result of this method call.
.RS
.PP
Note that this method is not exported by the \fBoo::class\fR object itself, so
classes should not be created using this method.
.RE
.SS "NON-EXPORTED METHODS"
.PP
The \fBoo::class\fR class supports the following non-exported methods:
.TP
\fIcls \fBcreateWithNamespace\fI name nsName\fR ?\fIarg ...\fR?
.
This creates a new instance of the class \fIcls\fR called \fIname\fR (which is
resolved within the calling context's namespace if not fully qualified),
passing the arguments, \fIarg ...\fR, to the constructor, and (if that returns
a successful result) returning the fully qualified name of the created object
(the result of the constructor is ignored). The name of the instance's
internal namespace will be \fInsName\fR;
.VS
it is an error if that namespace cannot be created.
.VE
If the constructor fails
(i.e., returns a non-OK result) then the object is destroyed and the error
message is the result of this method call.
.SH EXAMPLES
.PP
This example defines a simple class hierarchy and creates a new instance of
it. It then invokes a method of the object before destroying the hierarchy and
showing that the destruction is transitive.
.PP
.CS
\fBoo::class create\fR fruit {
    method eat {} {
        puts "yummy!"
    }
}
\fBoo::class create\fR banana {
    superclass fruit
    constructor {} {
        my variable peeled
        set peeled 0
    }
    method peel {} {
        my variable peeled
        set peeled 1
        puts "skin now off"
    }
    method edible? {} {
        my variable peeled
        return $peeled
    }
    method eat {} {
        if {![my edible?]} {
            my peel
        }
        next
    }
}
set b [banana \fBnew\fR]
$b eat               \fI\(-> prints "skin now off" and "yummy!"\fR
fruit destroy
$b eat               \fI\(-> error "unknown command"\fR
.CE
.SH "SEE ALSO"
oo::define(n), oo::object(n)
.SH KEYWORDS
class, metaclass, object
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