'\"
'\" Copyright (c) 2018 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 callback 3tcl 0.3 TclOO "TclOO Commands"
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'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
callback, mymethod \- generate callbacks to methods
.SH SYNOPSIS
.nf
package require tcl::oo

\fBcallback\fR \fImethodName\fR ?\fIarg ...\fR?
\fBmymethod\fR \fImethodName\fR ?\fIarg ...\fR?
.fi
.BE
.SH DESCRIPTION
The \fBcallback\fR command,
'\" Based on notes in the tcllib docs, we know the provenance of mymethod
also called \fBmymethod\fR for compatibility with the ooutil and snit packages
of Tcllib,
and which should only be used from within the context of a call to a method
(i.e. inside a method, constructor or destructor body) is used to generate a
script fragment that will invoke the method, \fImethodName\fR, on the current
object (as reported by \fBself\fR) when executed. Any additional arguments
provided will be provided as leading arguments to the callback. The resulting
script fragment shall be a proper list.
.PP
Note that it is up to the caller to ensure that the current object is able to
handle the call of \fImethodName\fR; this command does not check that.
\fImethodName\fR may refer to any exported or unexported method, but may not
refer to a private method as those can only be invoked directly from within
methods. If there is no such method present at the point when the callback is
invoked, the standard \fBunknown\fR method handler will be called.
.SH EXAMPLE
This is a simple echo server class. The \fBcallback\fR command is used in two
places, to arrange for the incoming socket connections to be handled by the
\fIAccept\fR method, and to arrange for the incoming bytes on those
connections to be handled by the \fIReceive\fR method.
.PP
.CS
oo::class create EchoServer {
    variable server clients
    constructor {port} {
        set server [socket -server [\fBcallback\fR Accept] $port]
        set clients {}
    }
    destructor {
        chan close $server
        foreach client [dict keys $clients] {
            chan close $client
        }
    }

    method Accept {channel clientAddress clientPort} {
        dict set clients $channel [dict create \e
                address $clientAddress port $clientPort]
        chan event $channel readable [\fBcallback\fR Receive $channel]
    }
    method Receive {channel} {
        if {[chan gets $channel line] >= 0} {
            my echo $channel $line
        } else {
            chan close $channel
            dict unset clients $channel
        }
    }

    method echo {channel line} {
        dict with clients $channel {
            chan puts $channel \e
                    [format {[%s:%d] %s} $address $port $line]
        }
    }
}
.CE
.SH "SEE ALSO"
chan(3tcl), fileevent(3tcl), my(3tcl), self(3tcl), socket(3tcl), trace(3tcl)
.SH KEYWORDS
callback, object
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