Learning zscript possible bad example given

[PlayTheDemO65]

so I pulled this code from https://zdoom.org/wiki/Converting_DECOR ... to_ZScript, I understand it well but the problem is it seems to have trouble with the "extend class Actor" it returns " line 6: Class Actor cannot be found in the current translation unit." so how would I convert this A_Dothis action and still have it usable to the entire cast of monsters and actors?

//===========================================================================
//
// Code (must be attached to Actor)
//
//===========================================================================
extend class Actor
{
void A_HeadAttack()
{
if (target)
{
if (CheckMeleeRange())
{
int damage = random[pr_headattack](1, 6) * 10;
A_PlaySound (AttackSound, CHAN_WEAPON);
int newdam = target.DamageMobj (self, self, damage, "Melee");
target.TraceBleed (newdam > 0 ? newdam : damage, self);
}
else
{
// launch a missile
SpawnMissile (target, "CacodemonBall");
}
}
}
}

[Apeirogon]

You can extend only classes that defined in same pack.
Actor class defined in gzdoom.pack, so you cant extend it in you mod.pack because its in separate pack.

And if you want to change how A_HeadAttack() works, you cant do so. Its not virtual so you cant redefine it.
If you want change something in it and use in you mod, all you can do is copy it into you mod, change it there and then use it at place of old a_headattack().

[PlayTheDemO65]

thank you!