Dispatch table

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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.

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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 a dispatch table in JavaScript:

constthingsWeCanDo={doThisThing(){/* behavior */},doThatThing(){/* behavior */},doThisOtherThing(){/* behavior */},default(){/* behavior */}};functiondoSomething(doWhat){constthingToDo=Object.hasOwn(thingsWeCanDo,doWhat)?doWhat:"default";returnthingsWeCanDo[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

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References

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