| '\" |
| '\" Copyright (c) 1993 The Regents of the University of California. |
| '\" Copyright (c) 1994-1997 Sun Microsystems, Inc. |
| '\" |
| '\" See the file "license.terms" for information on usage and redistribution |
| '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. |
| '\" |
| '\" RCS: @(#) $Id: upvar.n,v 1.5 2000/11/21 15:56:21 dkf Exp $ |
| '\" |
| '\" The 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 |
| '\" Start of list of standard options for a Tk widget. The |
| '\" options follow on successive lines, in four 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. |
| '\" |
| '\" RCS: @(#) $Id: man.macros,v 1.4 2000/08/25 06:18:32 ericm Exp $ |
| '\" |
| '\" # 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 |
| .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 \\fBoptions\\fR 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 |
| .. |
| .de UL |
| \\$1\l'|0\(ul'\\$2 |
| .. |
| .TH upvar n "" Tcl "Tcl Built-In Commands" |
| .BS |
| '\" Note: do not modify the .SH NAME line immediately below! |
| .SH NAME |
| upvar \- Create link to variable in a different stack frame |
| .SH SYNOPSIS |
| \fBupvar \fR?\fIlevel\fR? \fIotherVar myVar \fR?\fIotherVar myVar \fR...? |
| .BE |
| |
| .SH DESCRIPTION |
| .PP |
| This command arranges for one or more local variables in the current |
| procedure to refer to variables in an enclosing procedure call or |
| to global variables. |
| \fILevel\fR may have any of the forms permitted for the \fBuplevel\fR |
| command, and may be omitted if the first letter of the first \fIotherVar\fR |
| isn't \fB#\fR or a digit (it defaults to \fB1\fR). |
| For each \fIotherVar\fR argument, \fBupvar\fR makes the variable |
| by that name in the procedure frame given by \fIlevel\fR (or at |
| global level, if \fIlevel\fR is \fB#0\fR) accessible |
| in the current procedure by the name given in the corresponding |
| \fImyVar\fR argument. |
| The variable named by \fIotherVar\fR need not exist at the time of the |
| call; it will be created the first time \fImyVar\fR is referenced, just like |
| an ordinary variable. There must not exist a variable by the |
| name \fImyVar\fR at the time \fBupvar\fR is invoked. |
| \fIMyVar\fR is always treated as the name of a variable, not an |
| array element. Even if the name looks like an array element, |
| such as \fBa(b)\fR, a regular variable is created. |
| \fIOtherVar\fR may refer to a scalar variable, an array, |
| or an array element. |
| \fBUpvar\fR returns an empty string. |
| .PP |
| The \fBupvar\fR command simplifies the implementation of call-by-name |
| procedure calling and also makes it easier to build new control constructs |
| as Tcl procedures. |
| For example, consider the following procedure: |
| .CS |
| \fBproc add2 name { |
| upvar $name x |
| set x [expr $x+2] |
| }\fR |
| .CE |
| \fBAdd2\fR is invoked with an argument giving the name of a variable, |
| and it adds two to the value of that variable. |
| Although \fBadd2\fR could have been implemented using \fBuplevel\fR |
| instead of \fBupvar\fR, \fBupvar\fR makes it simpler for \fBadd2\fR |
| to access the variable in the caller's procedure frame. |
| .PP |
| \fBnamespace eval\fR is another way (besides procedure calls) |
| that the Tcl naming context can change. |
| It adds a call frame to the stack to represent the namespace context. |
| This means each \fBnamespace eval\fR command |
| counts as another call level for \fBuplevel\fR and \fBupvar\fR commands. |
| For example, \fBinfo level 1\fR will return a list |
| describing a command that is either |
| the outermost procedure call or the outermost \fBnamespace eval\fR command. |
| Also, \fBuplevel #0\fR evaluates a script |
| at top-level in the outermost namespace (the global namespace). |
| .PP |
| .VS |
| If an upvar variable is unset (e.g. \fBx\fR in \fBadd2\fR above), the |
| \fBunset\fR operation affects the variable it is linked to, not the |
| upvar variable. There is no way to unset an upvar variable except |
| by exiting the procedure in which it is defined. However, it is |
| possible to retarget an upvar variable by executing another \fBupvar\fR |
| command. |
| |
| .SH Traces and upvar |
| .PP |
| Upvar interacts with traces in a straightforward but possibly |
| unexpected manner. If a variable trace is defined on \fIotherVar\fR, that |
| trace will be triggered by actions involving \fImyVar\fR. However, |
| the trace procedure will be passed the name of \fImyVar\fR, rather |
| than the name of \fIotherVar\fR. Thus, the output of the following code |
| will be \fBlocalVar\fR rather than \fBoriginalVar\fR: |
| .CS |
| \fBproc traceproc { name index op } { |
| puts $name |
| } |
| proc setByUpvar { name value } { |
| upvar $name localVar |
| set localVar $value |
| } |
| set originalVar 1 |
| trace variable originalVar w traceproc |
| setByUpvar originalVar 2 |
| }\fR |
| .CE |
| |
| If \fIotherVar\fR refers to an element of an array, then variable |
| traces set for the entire array will not be invoked when \fImyVar\fR |
| is accessed (but traces on the particular element will still be |
| invoked). In particular, if the array is \fBenv\fR, then changes |
| made to \fImyVar\fR will not be passed to subprocesses correctly. |
| .VE |
| |
| .SH "SEE ALSO" |
| global(n), namespace(n), uplevel(n), variable(n) |
| |
| .SH KEYWORDS |
| context, frame, global, level, namespace, procedure, variable |