E07177: the super type has no accessible no-argument constructor (it is 'private', or there is none), so a default constructor cannot be generated here - you must define a constructor for this sub-type that calls an accessible super(...)

What went wrong

A sub-type defines no constructor at all, and its super has no accessible no-argument constructor: it is 'private', or there is none. EK9 would normally generate a public no-argument default constructor, but its hidden super() could not reach one - so no default is created and the type would be unconstructable.

A super has NO no-argument constructor when it is itself a sub-type of a base whose no-argument constructor is private: EK9 generates one only when the super has an accessible one, all the way down a chain.

How to fix it

1. Define a constructor for this sub-type that calls an accessible super(...) (the [EXAMPLE] section below: Sample takes an Integer and passes it on)
2. Or make the base's no-argument constructor accessible (public/protected)

Common causes

• Extending a base that declares 'default private Base()' (its properties are uninitialised, see E07175) without providing your own constructor
• Relying on the auto-generated no-argument default constructor, which cannot be created when the super's no-argument constructor is private or missing
• Extending a sub-type of such a base (a three-level chain): the middle type has no no-argument constructor either

See also

• E07176: a WRITTEN sub-type constructor that relies on the implicit super() when there is no accessible one
• E07175: default constructor must be 'private' when uninitialised properties exist
• EK9 does not mandate a no-argument constructor; a type may legitimately have none

Examples

Every example is compiled by the EK9 compiler: the first fails exactly as captioned, the others fix it.

Fails with E07177: the super type has no accessible no-argument constructor (it is 'private', or there is none), so a default constructor cannot be generated here - you must define a constructor for this sub-type that calls an accessible super(...)

#!ek9
defines module error.e07177.bad

  defines class

    Reading as open
      amount as Integer?

      default private Reading()

      Reading()
        -> initial as Integer
        this.amount: initial

      default operator ?

    //No constructor, and none can be generated: it would have to call the private Reading()
    Sample extends Reading
      describe()
        <- rtn as String: "a sample"

Fixed: Define a constructor that calls an accessible super(...)

#!ek9
defines module error.e07177.good

  defines class

    Reading as open
      amount as Integer?

      default private Reading()

      Reading()
        -> initial as Integer
        this.amount: initial

      default operator ?

    Sample extends Reading
      Sample()
        -> initial as Integer
        super(initial)

      describe()
        <- rtn as String: "a sample"

Questions and answers

These Q&A entries show E07177 and its fix:

• Q1353: How do I extend a base whose no-argument constructor is private (E07176 / E07177)?