Data Driven State Save/Restore

High Maintenance:

Drive state save/restore from a list of variables to save

Example: A set of save/restore procs

proc saveState {stateFile list} {
  set output [open $stateFile "w"]

  foreach variable $list { 
    eval "global $variable"
    puts $output "[list $variable [subst $$variable]]"
  }
  close $output
 }

proc restoreState {stateFile} {
  set input [open $stateFile "r"]
  while {![eof $input]} {
    set len [gets $input list]
    if {$len > 0} {
      eval "global [lindex $list 0]"
      eval "[list set [lindex $list 0] [lindex $list 1]]"
    } 
  }
  close $input
 }

Advantage:

• Provides full control of state variables to be saved/restored.

• Similar to familiar constructs used in "C" and Shell programming.

Disadvantage:

• Code must be modified when new state variables are added.

• Unnecessary processing must be done.

Low Maintenance:

Keep state in arrays, and use those indices to drive save/restore. Save state as a set of Tcl commands.

Example: A save proc, and associated restore call.

proc saveState {stateFile stateArray} {
  upvar $stateArray state 
  set output [open $stateFile "w"]
  puts $output "[list array set $stateArray [array get state]]"
  close $output
 }

# restore state
 source $stateFile

Advantage:

• New state variables are automatically saved and restored.

Disadvantage:

• All state indices are saved, whether you want them saved or not.

Use a naming convention define state indices to not save.

Example: A save proc, and associated restore call.

proc saveState {stateFile stateArray} {
  upvar $stateArray state 
  set output [open $stateFile "w"]

  foreach index [array names state] {
    if {[string first "nosave" $index] != 0} {
      puts $output "[list set $stateArray\ndex) $state($index)]"
    }
  }
  close $output
 }

# restore state
 source $stateFile

Advantage:

• Allows selection of state indices to not save

Disadvantage:

• Greater processor overhead.

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