ponylang: call constructor method in another constructor?

Question

ENV: ponylang 0.9.0

From ponylang tutorial

class Wombat
  let name: String
  var _hunger_level: U64

  new create(name': String) =>
    name = name'
    _hunger_level = 0

  new hungry(name': String, hunger': U64) =>
    name = name'
    _hunger_level = hunger'

tried following, compiler complains: constructor with undefined fields

  new create(name': String) =>
    hungry(name', 0)

Where to get an exact explanation?

Answer 1

A constructor call in Pony will always create a new object, there are no delegating constructors.

new create(name': String) =>
  hungry(name', 0)

In your example, the call to hungry isn't applied to the object being initialised in create, but to the new Wombat allocated.

In Pony pseudo-code, this is what's really happening.

new create(this: Wombat, name': String) =>
  let new_wombat = Wombat_Alloc()
  hungry(new_wombat, name', 0)