In computer science, a dispatch table is a table of pointers or memory addresses to functions or methods. 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-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 implementation
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 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
- Diomidis Spinellis (2003). Code Reading: The Open Source Perspective. Boston, MA: Addison-Wesley. ISBN 0-201-79940-5
References
Goldfuss, Alice. "Function Dispatch Tables in C". alicegoldfuss.com. Retrieved 23 January 2021. https://blog.alicegoldfuss.com/function-dispatch-tables/ ↩