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);subsay_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:

varthingsWeCanDo={doThisThing:function(){/* behavior */},doThatThing:function(){/* behavior */},doThisOtherThing:function(){/* behavior */},default:function(){/* behavior */}};vardoSomething=function(doWhat){varthingToDo=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