UpvarExistingOrDie

NAME

UpvarExistingOrDie — Do upvar if variable exists, else generate error.

SYNOPSIS

UpvarExistingOrDie VarName Var

DESCRIPTION

Return Value

None (empty string).

Arguments

VarName	Name of variable to check for and upvar (same as first argument to upvar).
Var	Name of variable after upvar (same as second argument to upvar).

More Info

The way upvar works, it will automatically create a variable if it does not exist. If this is not desired, you can use this command to check for an expected variable and if it is not there then generate an error.

For information regarding exceptions / errors, see here.

EXAMPLES

The following code creates a proc that relies on variable existing. When it does not exist, UpvarExistingOrDie will create an error.

proc MyPrintVar {VarName} {
     UpvarExistingOrDie $VarName Var
     puts "$VarName = $Var"
}

% set abc 123
% MyPrintVar abc
abc = 123
% unset abc
% MyPrintVar abc
Could not find variable abc.