distrib/share/tcl/help/tcl/variables/variable

   1 NAME
   2        variable - create and initialize a namespace variable
   3
   4 SYNOPSIS
   5        variable ?name value...? name ?value?
   6
   7
   8 DESCRIPTION
   9        This command is normally used within a namespace eval command to create
  10        one or more variables within a namespace.  Each variable name  is  ini-
  11        tialized with value.  The value for the last variable is optional.
  12
  13        If  a  variable  name  does not exist, it is created.  In this case, if
  14        value is specified, it is assigned to the newly created  variable.   If
  15        no  value  is  specified,  the  new variable is left undefined.  If the
  16        variable already exists, it is set to value if value  is  specified  or
  17        left  unchanged  if  no  value is given.  Normally, name is unqualified
  18        (does not include the names of  any  containing  namespaces),  and  the
  19        variable  is  created  in  the current namespace.  If name includes any
  20        namespace qualifiers, the variable is created in the  specified  names-
  21        pace.  If the variable is not defined, it will be visible to the names-
  22        pace which command, but not to the info exists command.
  23
  24        If the variable command is executed inside a Tcl procedure, it  creates
  25        local  variables  linked  to the corresponding namespace variables (and
  26        therefore these variables are listed by info vars.)  In  this  way  the
  27        variable command resembles the global command, although the global com-
  28        mand only links to variables in the global namespace.   If  any  values
  29        are  given, they are used to modify the values of the associated names-
  30        pace variables.  If a namespace variable does not exist, it is  created
  31        and optionally initialized.
  32
  33        A  name argument cannot reference an element within an array.  Instead,
  34        name should reference the entire array, and  the  initialization  value
  35        should  be  left  off.   After the variable has been declared, elements
  36        within the array can be set using ordinary set or array commands.
  37
  38 EXAMPLES
  39        Create a variable in a namespace:
  40               namespace eval foo {
  41                   variable bar 12345
  42               }
  43
  44        Create an array in a namespace:
  45               namespace eval someNS {
  46                   variable someAry
  47                   array set someAry {
  48                       someName  someValue
  49                       otherName otherValue
  50                   }
  51               }
  52
  53        Access variables in namespaces from a procedure:
  54               namespace eval foo {
  55                   proc spong {} {
  56                       # Variable in this namespace
  57                       variable bar
  58                       puts "bar is $bar"
  59
  60                       # Variable in another namespace
  61                       variable ::someNS::someAry
  62                       parray someAry
  63                   }
  64               }
  65
  66
  67 SEE ALSO
  68        global(n), namespace(n), upvar(n)
  69
  70
  71 KEYWORDS