--- /dev/null
+'\"
+'\" 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 next n 0.1 TclOO "TclOO Commands"
+.\" The -*- nroff -*- definitions below are for supplemental macros used
+.\" in Tcl/Tk manual entries.
+.\"
+.\" .AP type name in/out ?indent?
+.\" Start paragraph describing an argument to a library procedure.
+.\" type is type of argument (int, etc.), in/out is either "in", "out",
+.\" or "in/out" to describe whether procedure reads or modifies arg,
+.\" and indent is equivalent to second arg of .IP (shouldn't ever be
+.\" needed; use .AS below instead)
+.\"
+.\" .AS ?type? ?name?
+.\" Give maximum sizes of arguments for setting tab stops. Type and
+.\" name are examples of largest possible arguments that will be passed
+.\" to .AP later. If args are omitted, default tab stops are used.
+.\"
+.\" .BS
+.\" Start box enclosure. From here until next .BE, everything will be
+.\" enclosed in one large box.
+.\"
+.\" .BE
+.\" End of box enclosure.
+.\"
+.\" .CS
+.\" Begin code excerpt.
+.\"
+.\" .CE
+.\" End code excerpt.
+.\"
+.\" .VS ?version? ?br?
+.\" Begin vertical sidebar, for use in marking newly-changed parts
+.\" of man pages. The first argument is ignored and used for recording
+.\" the version when the .VS was added, so that the sidebars can be
+.\" found and removed when they reach a certain age. If another argument
+.\" is present, then a line break is forced before starting the sidebar.
+.\"
+.\" .VE
+.\" End of vertical sidebar.
+.\"
+.\" .DS
+.\" Begin an indented unfilled display.
+.\"
+.\" .DE
+.\" End of indented unfilled display.
+.\"
+.\" .SO ?manpage?
+.\" Start of list of standard options for a Tk widget. The manpage
+.\" argument defines where to look up the standard options; if
+.\" omitted, defaults to "options". The options follow on successive
+.\" lines, in three columns separated by tabs.
+.\"
+.\" .SE
+.\" End of list of standard options for a Tk widget.
+.\"
+.\" .OP cmdName dbName dbClass
+.\" Start of description of a specific option. cmdName gives the
+.\" option's name as specified in the class command, dbName gives
+.\" the option's name in the option database, and dbClass gives
+.\" the option's class in the option database.
+.\"
+.\" .UL arg1 arg2
+.\" Print arg1 underlined, then print arg2 normally.
+.\"
+.\" .QW arg1 ?arg2?
+.\" Print arg1 in quotes, then arg2 normally (for trailing punctuation).
+.\"
+.\" .PQ arg1 ?arg2?
+.\" Print an open parenthesis, arg1 in quotes, then arg2 normally
+.\" (for trailing punctuation) and then a closing parenthesis.
+.\"
+.\" # Set up traps and other miscellaneous stuff for Tcl/Tk man pages.
+.if t .wh -1.3i ^B
+.nr ^l \n(.l
+.ad b
+.\" # Start an argument description
+.de AP
+.ie !"\\$4"" .TP \\$4
+.el \{\
+. ie !"\\$2"" .TP \\n()Cu
+. el .TP 15
+.\}
+.ta \\n()Au \\n()Bu
+.ie !"\\$3"" \{\
+\&\\$1 \\fI\\$2\\fP (\\$3)
+.\".b
+.\}
+.el \{\
+.br
+.ie !"\\$2"" \{\
+\&\\$1 \\fI\\$2\\fP
+.\}
+.el \{\
+\&\\fI\\$1\\fP
+.\}
+.\}
+..
+.\" # define tabbing values for .AP
+.de AS
+.nr )A 10n
+.if !"\\$1"" .nr )A \\w'\\$1'u+3n
+.nr )B \\n()Au+15n
+.\"
+.if !"\\$2"" .nr )B \\w'\\$2'u+\\n()Au+3n
+.nr )C \\n()Bu+\\w'(in/out)'u+2n
+..
+.AS Tcl_Interp Tcl_CreateInterp in/out
+.\" # BS - start boxed text
+.\" # ^y = starting y location
+.\" # ^b = 1
+.de BS
+.br
+.mk ^y
+.nr ^b 1u
+.if n .nf
+.if n .ti 0
+.if n \l'\\n(.lu\(ul'
+.if n .fi
+..
+.\" # BE - end boxed text (draw box now)
+.de BE
+.nf
+.ti 0
+.mk ^t
+.ie n \l'\\n(^lu\(ul'
+.el \{\
+.\" Draw four-sided box normally, but don't draw top of
+.\" box if the box started on an earlier page.
+.ie !\\n(^b-1 \{\
+\h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul'
+.\}
+.el \}\
+\h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul'
+.\}
+.\}
+.fi
+.br
+.nr ^b 0
+..
+.\" # VS - start vertical sidebar
+.\" # ^Y = starting y location
+.\" # ^v = 1 (for troff; for nroff this doesn't matter)
+.de VS
+.if !"\\$2"" .br
+.mk ^Y
+.ie n 'mc \s12\(br\s0
+.el .nr ^v 1u
+..
+.\" # VE - end of vertical sidebar
+.de VE
+.ie n 'mc
+.el \{\
+.ev 2
+.nf
+.ti 0
+.mk ^t
+\h'|\\n(^lu+3n'\L'|\\n(^Yu-1v\(bv'\v'\\n(^tu+1v-\\n(^Yu'\h'-|\\n(^lu+3n'
+.sp -1
+.fi
+.ev
+.\}
+.nr ^v 0
+..
+.\" # Special macro to handle page bottom: finish off current
+.\" # box/sidebar if in box/sidebar mode, then invoked standard
+.\" # page bottom macro.
+.de ^B
+.ev 2
+'ti 0
+'nf
+.mk ^t
+.if \\n(^b \{\
+.\" Draw three-sided box if this is the box's first page,
+.\" draw two sides but no top otherwise.
+.ie !\\n(^b-1 \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c
+.el \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c
+.\}
+.if \\n(^v \{\
+.nr ^x \\n(^tu+1v-\\n(^Yu
+\kx\h'-\\nxu'\h'|\\n(^lu+3n'\ky\L'-\\n(^xu'\v'\\n(^xu'\h'|0u'\c
+.\}
+.bp
+'fi
+.ev
+.if \\n(^b \{\
+.mk ^y
+.nr ^b 2
+.\}
+.if \\n(^v \{\
+.mk ^Y
+.\}
+..
+.\" # DS - begin display
+.de DS
+.RS
+.nf
+.sp
+..
+.\" # DE - end display
+.de DE
+.fi
+.RE
+.sp
+..
+.\" # SO - start of list of standard options
+.de SO
+'ie '\\$1'' .ds So \\fBoptions\\fR
+'el .ds So \\fB\\$1\\fR
+.SH "STANDARD OPTIONS"
+.LP
+.nf
+.ta 5.5c 11c
+.ft B
+..
+.\" # SE - end of list of standard options
+.de SE
+.fi
+.ft R
+.LP
+See the \\*(So manual entry for details on the standard options.
+..
+.\" # OP - start of full description for a single option
+.de OP
+.LP
+.nf
+.ta 4c
+Command-Line Name: \\fB\\$1\\fR
+Database Name: \\fB\\$2\\fR
+Database Class: \\fB\\$3\\fR
+.fi
+.IP
+..
+.\" # CS - begin code excerpt
+.de CS
+.RS
+.nf
+.ta .25i .5i .75i 1i
+..
+.\" # CE - end code excerpt
+.de CE
+.fi
+.RE
+..
+.\" # UL - underline word
+.de UL
+\\$1\l'|0\(ul'\\$2
+..
+.\" # QW - apply quotation marks to word
+.de QW
+.ie '\\*(lq'"' ``\\$1''\\$2
+.\"" fix emacs highlighting
+.el \\*(lq\\$1\\*(rq\\$2
+..
+.\" # PQ - apply parens and quotation marks to word
+.de PQ
+.ie '\\*(lq'"' (``\\$1''\\$2)\\$3
+.\"" fix emacs highlighting
+.el (\\*(lq\\$1\\*(rq\\$2)\\$3
+..
+.\" # QR - quoted range
+.de QR
+.ie '\\*(lq'"' ``\\$1''\\-``\\$2''\\$3
+.\"" fix emacs highlighting
+.el \\*(lq\\$1\\*(rq\\-\\*(lq\\$2\\*(rq\\$3
+..
+.\" # MT - "empty" string
+.de MT
+.QW ""
+..
+.BS
+'\" Note: do not modify the .SH NAME line immediately below!
+.SH NAME
+next, nextto \- invoke superclass method implementations
+.SH SYNOPSIS
+.nf
+package require TclOO
+
+\fBnext\fR ?\fIarg ...\fR?
+\fBnextto\fI class\fR ?\fIarg ...\fR?
+.fi
+.BE
+
+.SH DESCRIPTION
+.PP
+The \fBnext\fR command is used to call implementations of a method by a class,
+superclass or mixin that are overridden by the current method. It can only be
+used from within a method. It is also used within filters to indicate the
+point where a filter calls the actual implementation (the filter may decide to
+not go along the chain, and may process the results of going along the chain
+of methods as it chooses). The result of the \fBnext\fR command is the result
+of the next method in the method chain; if there are no further methods in the
+method chain, the result of \fBnext\fR will be an error. The arguments,
+\fIarg\fR, to \fBnext\fR are the arguments to pass to the next method in the
+chain.
+.PP
+The \fBnextto\fR command is the same as the \fBnext\fR command, except that it
+takes an additional \fIclass\fR argument that identifies a class whose
+implementation of the current method chain (see \fBinfo object\fR \fBcall\fR) should
+be used; the method implementation selected will be the one provided by the
+given class, and it must refer to an existing non-filter invocation that lies
+further along the chain than the current implementation.
+.SH "THE METHOD CHAIN"
+.PP
+When a method of an object is invoked, things happen in several stages:
+.IP [1]
+The structure of the object, its class, superclasses, filters, and mixins, are
+examined to build a \fImethod chain\fR, which contains a list of method
+implementations to invoke.
+.IP [2]
+The first method implementation on the chain is invoked.
+.IP [3]
+If that method implementation invokes the \fBnext\fR command, the next method
+implementation is invoked (with its arguments being those that were passed to
+\fBnext\fR).
+.IP [4]
+The result from the overall method call is the result from the outermost
+method implementation; inner method implementations return their results
+through \fBnext\fR.
+.IP [5]
+The method chain is cached for future use.
+.SS "METHOD SEARCH ORDER"
+.PP
+When constructing the method chain, method implementations are searched for in
+the following order:
+.IP [1]
+In the classes mixed into the object, in class traversal order. The list of
+mixins is checked in natural order.
+.IP [2]
+In the classes mixed into the classes of the object, with sources of mixing in
+being searched in class traversal order. Within each class, the list of mixins
+is processed in natural order.
+.IP [3]
+In the object itself.
+.IP [4]
+In the object's class.
+.IP [5]
+In the superclasses of the class, following each superclass in a depth-first
+fashion in the natural order of the superclass list.
+.PP
+Any particular method implementation always comes as \fIlate\fR in the
+resulting list of implementations as possible; this means that if some class,
+A, is both mixed into a class, B, and is also a superclass of B, the instances
+of B will always treat A as a superclass from the perspective of inheritance.
+This is true even when the multiple inheritance is processed indirectly.
+.SS FILTERS
+.PP
+When an object has a list of filter names set upon it, or is an instance of a
+class (or has mixed in a class) that has a list of filter names set upon it,
+before every invocation of any method the filters are processed. Filter
+implementations are found in class traversal order, as are the lists of filter
+names (each of which is traversed in natural list order). Explicitly invoking
+a method used as a filter will cause that method to be invoked twice, once as
+a filter and once as a normal method.
+.PP
+Each filter should decide for itself whether to permit the execution to go
+forward to the proper implementation of the method (which it does by invoking
+the \fBnext\fR command as filters are inserted into the front of the method
+call chain) and is responsible for returning the result of \fBnext\fR.
+.PP
+Filters are invoked when processing an invokation of the \fBunknown\fR
+method because of a failure to locate a method implementation, but \fInot\fR
+when invoking either constructors or destructors. (Note however that the
+\fBdestroy\fR method is a conventional method, and filters are invoked as
+normal when it is called.)
+.SH EXAMPLES
+.PP
+This example demonstrates how to use the \fBnext\fR command to call the
+(super)class's implementation of a method. The script:
+.PP
+.CS
+oo::class create theSuperclass {
+ method example {args} {
+ puts "in the superclass, args = $args"
+ }
+}
+oo::class create theSubclass {
+ superclass theSuperclass
+ method example {args} {
+ puts "before chaining from subclass, args = $args"
+ \fBnext\fR a {*}$args b
+ \fBnext\fR pureSynthesis
+ puts "after chaining from subclass"
+ }
+}
+theSubclass create obj
+oo::objdefine obj method example args {
+ puts "per-object method, args = $args"
+ \fBnext\fR x {*}$args y
+ \fBnext\fR
+}
+obj example 1 2 3
+.CE
+.PP
+prints the following:
+.PP
+.CS
+per-object method, args = 1 2 3
+before chaining from subclass, args = x 1 2 3 y
+in the superclass, args = a x 1 2 3 y b
+in the superclass, args = pureSynthesis
+after chaining from subclass
+before chaining from subclass, args =
+in the superclass, args = a b
+in the superclass, args = pureSynthesis
+after chaining from subclass
+.CE
+.PP
+This example demonstrates how to build a simple cache class that applies
+memoization to all the method calls of the objects it is mixed into, and shows
+how it can make a difference to computation times:
+.PP
+.CS
+oo::class create cache {
+ filter Memoize
+ method Memoize args {
+ \fI# Do not filter the core method implementations\fR
+ if {[lindex [self target] 0] eq "::oo::object"} {
+ return [\fBnext\fR {*}$args]
+ }
+
+ \fI# Check if the value is already in the cache\fR
+ my variable ValueCache
+ set key [self target],$args
+ if {[info exist ValueCache($key)]} {
+ return $ValueCache($key)
+ }
+
+ \fI# Compute value, insert into cache, and return it\fR
+ return [set ValueCache($key) [\fBnext\fR {*}$args]]
+ }
+ method flushCache {} {
+ my variable ValueCache
+ unset ValueCache
+ \fI# Skip the caching\fR
+ return -level 2 ""
+ }
+}
+
+oo::object create demo
+oo::objdefine demo {
+ mixin cache
+ method compute {a b c} {
+ after 3000 \fI;# Simulate deep thought\fR
+ return [expr {$a + $b * $c}]
+ }
+ method compute2 {a b c} {
+ after 3000 \fI;# Simulate deep thought\fR
+ return [expr {$a * $b + $c}]
+ }
+}
+
+puts [demo compute 1 2 3] \fI\(-> prints "7" after delay\fR
+puts [demo compute2 4 5 6] \fI\(-> prints "26" after delay\fR
+puts [demo compute 1 2 3] \fI\(-> prints "7" instantly\fR
+puts [demo compute2 4 5 6] \fI\(-> prints "26" instantly\fR
+puts [demo compute 4 5 6] \fI\(-> prints "34" after delay\fR
+puts [demo compute 4 5 6] \fI\(-> prints "34" instantly\fR
+puts [demo compute 1 2 3] \fI\(-> prints "7" instantly\fR
+demo flushCache
+puts [demo compute 1 2 3] \fI\(-> prints "7" after delay\fR
+.CE
+.SH "SEE ALSO"
+oo::class(n), oo::define(n), oo::object(n), self(n)
+.SH KEYWORDS
+call, method, method chain
+.\" Local variables:
+.\" mode: nroff
+.\" fill-column: 78
+.\" End:
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