diff options
Diffstat (limited to 'doc/upvar.n')
| -rw-r--r-- | doc/upvar.n | 62 |
1 files changed, 32 insertions, 30 deletions
diff --git a/doc/upvar.n b/doc/upvar.n index bb25fee..380a390 100644 --- a/doc/upvar.n +++ b/doc/upvar.n @@ -5,10 +5,8 @@ '\" 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 1.7 2004/05/18 21:29:22 dkf Exp $ -'\" -.so man.macros .TH upvar n "" Tcl "Tcl Built-In Commands" +.so man.macros .BS '\" Note: do not modify the .SH NAME line immediately below! .SH NAME @@ -23,8 +21,7 @@ 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). +command, and may be omitted (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 @@ -45,16 +42,18 @@ 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: +.PP .CS -\fBproc add2 name { - upvar $name x - set x [expr $x+2] -}\fR +proc \fIadd2\fR name { + \fBupvar\fR $name x + set x [expr {$x + 2}] +} .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 +.PP +If \fIadd2\fR is invoked with an argument giving the name of a variable, +it adds two to the value of that variable. +Although \fIadd2\fR could have been implemented using \fBuplevel\fR +instead of \fBupvar\fR, \fBupvar\fR makes it simpler for \fIadd2\fR to access the variable in the caller's procedure frame. .PP \fBnamespace eval\fR is another way (besides procedure calls) @@ -62,13 +61,12 @@ 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 +For example, \fBinfo level\fR \fB1\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 @@ -82,39 +80,43 @@ 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: +will be +.QW "\fIlocalVar\fR" +rather than +.QW "\fIoriginalVar\fR" : +.PP .CS -\fBproc traceproc { name index op } { - puts $name +proc \fItraceproc\fR { name index op } { + puts $name } -proc setByUpvar { name value } { - upvar $name localVar - set localVar $value +proc \fIsetByUpvar\fR { name value } { + \fBupvar\fR $name localVar + set localVar $value } set originalVar 1 -trace variable originalVar w traceproc -setByUpvar originalVar 2 -}\fR +trace variable originalVar w \fItraceproc\fR +\fIsetByUpvar\fR originalVar 2 .CE - +.PP 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 EXAMPLE A \fBdecr\fR command that works like \fBincr\fR except it subtracts the value from the variable instead of adding it: +.PP .CS proc decr {varName {decrement 1}} { - upvar 1 $varName var + \fBupvar\fR 1 $varName var incr var [expr {-$decrement}] } .CE - .SH "SEE ALSO" global(n), namespace(n), uplevel(n), variable(n) - .SH KEYWORDS -context, frame, global, level, namespace, procedure, variable +context, frame, global, level, namespace, procedure, upvar, variable +.\" Local Variables: +.\" mode: nroff +.\" End: |