In order to use Polymorphism (and dynamic dispatch in particular) with templates you should be able to define templates on entities.

Currently we can do something polymorphic with functions only, so:

entity Base {
}

define output(b: Base) {
// show simple output
}

entity Sub : Base {
function foo() {
// do something
}
}

define output(s: Sub) {
// show custom output for sub
}

define page doSomething(b: Base) {
init {
b.foo(); // this works
}
main {
output(b) // this does not call output(s: Sub)
}
}

An option would be to define a function on an entity, such as:

extend entity Sub {
define show() {
// show custom output for sub
}
}

And then in doSomething we can call b.show() instead of output(b).

Submitted by Tim on 18 March 2010 at 11:25

I’ve also proposed this a while ago, another advantage is that the plugin could then provide relevant templatecall completions once you type b. in the body of a template. It would also be easy to implement since it just reuses Java dispatch like we do now with the entity functions.

A recurring discussion related to this is whether it is worth the effort to implement multiple dispatch for templates (and functions) instead of relying on the Java dispatch semantics.