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 pointers or memory addresses to functions or methods.{{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}} 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 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 =
Following is a demo of implementing a dispatch table in 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]();
}
Virtual method tables
{{Main|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
References
{{reflist}}
- Diomidis Spinellis (2003). Code Reading: The Open Source Perspective. Boston, MA: Addison-Wesley. {{ISBN|0-201-79940-5}}