E05050: 'this()' and 'super()' must be the first statement in a constructor

What went wrong

Calls to this() or super() must be the FIRST statement in a constructor. You have code executing before the constructor delegation call. This violates the initialization order requirement.

Worked examples

Compilable examples demonstrating this error and the correct fix:

• ek9 -q 582 (Why must this() or super() be the first statement in a co...)
• ek9 -q 580 (How do I call one constructor from another using this()?)
• ek9 -q 581 (How do I call a parent constructor using super()?)
• ek9 -q 583 (Can I use both this() and super() in the same constructor?)
• ek9 -q 584 (When is an explicit super() call required?)

How to fix it

1. Move this() or super() to be the very first statement
2. Any parameter validation must come AFTER the delegating call
3. If validation must happen first, do it in the delegated constructor

Rationale

This rule ensures:

• Object is properly initialized before any other code runs
• Parent class state is established before child accesses it
• Field initialization order is consistent and predictable

Common causes

• Wanting to validate parameters before delegation
• Copying patterns from languages with different rules
• Refactoring that moved statements around

See also

• E05050: delegation not first statement (this error)
• E05040: super() without explicit parent (no parent to delegate to)
• E05060: this()/super() outside constructor (wrong context)

Examples

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

Fails with E05050: 'this()' and 'super()' must be the first statement in a constructor

#!ek9
defines module error.e05050.bad

  defines class

    Base as open
      label as String: "base"

      Base()
        -> label as String
        this.label: label

      default operator ?

    Derived extends Base
      extra as String: "derived"

      Derived()
        -> label as String
        super(label)
        //Construction delegates once, first: a second call is not first
        super(label)

      Derived()
        ->
          label as String
          extra as String

        this.extra: extra
        this(label)

      default operator ?

Fixed: Call super(...) or this(...) once, as the first statement; other work follows it

#!ek9
defines module error.e05050.good

  defines class

    Base as open
      label as String: "base"

      Base()
        -> label as String
        this.label: label

      default operator ?

    Derived extends Base
      extra as String: "derived"

      Derived()
        -> label as String
        super(label)

      Derived()
        ->
          label as String
          extra as String

        this(label)
        this.extra: extra

      default operator ?

Questions and answers

These Q&A entries show E05050 and its fix:

• Q580: How do I call one constructor from another using this()?
• Q581: How do I call a parent constructor using super()?
• Q582: Why must this() or super() be the first statement in a constructor?
• Q583: Can I use both this() and super() in the same constructor?
• Q584: When is an explicit super() call required?
• Q586: How does constructor delegation work with pure constructors?
• Q587: How do constructors work in multi-level class hierarchies?
• Q591: How do function hierarchies compare to class hierarchies?
• Q598: Why doesn't EK9 have default parameter values?
• Q679: How do sealed classes with allow only work in EK9?