Dispatch table

In computer science, a dispatch table is a table of pointers or memory addresses to functions or methods.^[1] Use of such a table is a common technique when implementing late binding in object-oriented programming.

Perl implementation

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

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"  thingsWeCanDo[thingToDo](); } 

Virtual method tables

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

• Branch table

References

1. Goldfuss, Alice. "Function Dispatch Tables in C". alicegoldfuss.com. Retrieved 23 January 2021.

• Diomidis Spinellis (2003). Code Reading: The Open Source Perspective. Boston, MA: Addison-Wesley. ISBN 0-201-79940-5