E07070: traits do not support constructor methods

What went wrong

You're defining a constructor in a TRAIT, but traits cannot have constructors - only classes can create instances.

Worked examples

Compilable examples demonstrating this error and the correct fix:

• ek9 -q 106 (What are traits and how do I use them in EK9?)

How to fix it

1. Remove constructor from trait
2. Use default values for initialization
3. Move construction logic to implementing class

Common causes

• Treating trait like a class
• Trying to initialize trait state
• Misunderstanding trait capabilities

See also

• E07070: constructor in trait (this error)
• E07030: default operator in trait
• E07040: 'by' delegation in trait

Examples

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

Fails with E07070: traits do not support constructor methods

#!ek9
defines module error.e07070.bad

  defines trait
    Nameable

      //A trait is never constructed on its own
      Nameable()

Fixed: Construct the class that has the trait

#!ek9
defines module error.e07070.good

  defines trait
    Nameable
      name() as abstract
        <- rtn as String?

  defines class
    Person with trait of Nameable
      personName as String?

      default private Person()

      Person()
        -> newName as String
        this.personName: newName

      override name()
        <- rtn as String: personName

      default operator ?

Questions and answers

These Q&A entries show E07070 and its fix:

• Q106: What are traits and how do I use them in EK9?