Dispatch table

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In computer science, a dispatch table is a table of pointers to functions or methods. Use of such a table is a common technique when implementing late binding in object-oriented programming.

Perl implementation[edit]

The following shows one way to implement a dispatch table in Perl, using a hash to store references to code (also known as function pointers).

 #define the table using one anonymous code-ref and one named code-ref
 my %dispatch = (
   "-h" => sub {  return "hello\n"; },
   "-g" => \&say_goodbye
 sub say_goodbye {
   return "goodbye\n";
 #fetch the code ref from the table, and invoke it
 my $sub = $dispatch{$ARGV[0]};
 print $sub ? $sub->() : "unknown argument\n";

Running this Perl program as perl greet -h will produce "hello", and running it as perl greet -g will produce "goodbye".

Javascript implementation[edit]

Following is a demo of implementing Dispatch table in Javascript:

var thingsWeCanDo = {
    doThisThing      : function() { /* behavior */ },
    doThatThing      : function() { /* behavior */ },
    doThisOtherThing : function() { /* behavior */ },
    default          : function() { /* behavior */ }

var doSomething = function(doWhat) {
    var thingToDo = thingsWeCanDo.hasOwnProperty(doWhat) ? doWhat : "default"

Virtual method tables[edit]

Main article: Virtual method table

In object-oriented programming languages that support virtual methods, the compiler will automatically create a dispatch table for each object of a class containing virtual methods. This table is called a virtual method table or vtable, and every call to a virtual method is dispatched through the vtable.

See also[edit]