ensemble extend

Here's a simple bit of code to extend any ensemble-like command by means of tcl8.5's namespace ensemble command. CMcC 6Mar2006

Larry Smith: stacking does a similar job.

 package provide extend 1.0
 package require Tcl 8.5
 
 # extend a command with a new subcommand
 proc extend {cmd body} {
    if {![namespace exists ${cmd}]} {
        set wrapper [string map [list %C $cmd %B $body] {
            namespace eval %C {}
            rename %C %C::%C
            namespace eval %C {
                proc _unknown {junk subc args} {
                    return [list %C::%C $subc]
                }
                namespace ensemble create -unknown %C::_unknown
            }
        }]
    }

    append wrapper [string map [list %C $cmd %B $body] {
        namespace eval %C {
            %B
            namespace export -clear *
        }
    }]
    uplevel 1 $wrapper
 }

Here's the file command extended with newer and newerthan subcommands:

 extend file {
    proc newer {a b} {
       return [expr {[file mtime $a] > [file mtime $b]}]
    }

    proc newerthan {mtime path} {
       return [expr {[file exists $path] && ([file mtime $path] > $mtime)}]
    }
 }

Here's the dict command extended with the modify subcommand:

 # extra useful dict commands
 extend dict {
    proc modify {var args} {
       upvar 1 $var dvar
       foreach {name val} $args {
          dict set dvar $name $val
       }
    }
 }

LV So, this seems like a nice bit of functionality. Would it be useful enough to include either in Tcl itself or at least Tcllib?

quick hacks ?

AMG: See also my [dict getnull] example in [dict get].

Category Example