[Richard Suchenwirth] 2002-11-15 - I still remember how [Cameron Laird] groaned at me when I showed how to simulate [array]s of function pointers (Tcl's equivalent being the names of functions, [everything is a string]). After re-reading man Tcl last night (always recommended, even after years in the business ;-), it dawned on me this morning that we don't have to simulate that - using Tcl's substitution rules, we just have it. Consider:
 #--------------------------------- dummy procs as playing material
 proc eat    x {puts "eating $x"}
 proc drink  x {puts "drinking $x"}
 proc inhale x {puts "inhaling $x"}

 #---------------------------------- building the mapping table
 array set fp {
     liquid  drink
     solid   eat
     gaseous inhale
 }
 #---------------------------------- testing:
 foreach {state matter} {solid bread  liquid wine  gaseous perfume} {
     $fp($state) $matter
 }
 #------------------- results in:
 eating bread
 drinking wine
 inhaling perfume

What happens to $fp($state)? First $state is substituted, as is the rule with arrays. Then the array element e.g. $fp(solid) is looked up in the array, and its result makes the command name ''eat'', which finally is executed with the argument e.g. ''bread''.
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15nov2002 [KPV] - funny, I use an array of function pointers in the [M�ir� Patterns] program I posted here just yesterday. I needed to draw the foreground or background as one of several patterns and I wanted an easy way to make this extensible. So I just created an array of function pointers, and now to add a new type is just write the subroutine and add its name and ''reference'' to the array. Furthermore, in the GUI widget where the
user can select the type, I just use ''[[array names fptr]]'' to get the
list. Below is the relevant code snippets:

 array set fptr {"Parallel Lines" Parallel "Radial Lines" Radial \
                    Circles Circles}

 proc Show {who angle} {
    global fptr SS
    $fptr($SS($who,type)) $who $angle
 }

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[Category Concept] | [Arts and crafts of Tcl-Tk programming]