Editing Dispatch table

{{Short description|Computer code structure with a table of pointers to functions or similar}}
In [[computer science]], a '''dispatch table''' is a table of [[pointer (computer programming)|pointer]]s or [[memory address]]es to functions or [[method (computer science)|method]]s.<ref>{{cite web |last1=Goldfuss |first1=Alice |title=Function Dispatch Tables in C |url=https://blog.alicegoldfuss.com/function-dispatch-tables/ |website=alicegoldfuss.com |access-date=23 January 2021}}</ref>  Use of such a table is a common technique when implementing [[late binding]] in [[object-oriented programming]].

== In different programming languages ==
=== Perl ===
The following shows one way to implement a dispatch table in [[Perl]], using a [[Associative array#Perl|hash]] to store references to code (also known as [[function pointer]]s).

<syntaxhighlight lang="perl">
# 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";
</syntaxhighlight>

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

=== JavaScript ===
Following is a demo of implementing a dispatch table in JavaScript:
<syntaxhighlight lang="javascript">
const thingsWeCanDo = {
    doThisThing() { /* behavior */ },
    doThatThing() { /* behavior */ },
    doThisOtherThing() { /* behavior */ },
    default() { /* behavior */ }
};

function doSomething(doWhat) {
    const thingToDo = Object.hasOwn(thingsWeCanDo, doWhat) 
        ? doWhat 
        : "default";
    return thingsWeCanDo[thingToDo]();
}
</syntaxhighlight>

== Virtual method tables ==
{{Main|Virtual method table}}
In [[object-oriented programming|object-oriented]] [[programming language]]s that support [[virtual method]]s, the [[compiler]] will automatically create a dispatch table for each object of a [[class (computer science)|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 ==
{{reflist}}
* [[Diomidis Spinellis]] (2003). ''[[Code Reading]]: The Open Source Perspective''. Boston, MA: Addison-Wesley. {{ISBN|0-201-79940-5}}

[[Category:Method (computer programming)]]
[[Category:Articles with example Perl code]]