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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-refmy %dispatch = ( "-h" => sub { return "hello\n"; }, "-g" => \&say_goodbye); sub say_goodbye { return "goodbye\n";} # Fetch the code ref from the table, and invoke itmy $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

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

References

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