E02050: same trait referenced multiple times

What went wrong

The same trait is listed multiple times in a 'with trait of' clause. Each trait should only appear once in the declaration. Every trait listed more than once is named in the one error ('T1', 'T2').

Worked examples

Compilable examples demonstrating this error and the correct fix:

• ek9 -q 740 (How does EK9 detect duplicate trait references and servic...)

How to fix it

• Remove the duplicate trait from the list
• Check for same trait via different paths (module::T1 vs T1)

Common causes

• Copy-paste error in trait list
• Same trait referenced with and without module qualifier

Note

The same trait CAN be reached more than once through the INHERITANCE hierarchy (two different listed traits that share it - a diamond). This error is specifically about direct duplicate listing in a single 'with trait of' clause; listing a trait that another listed trait, or the super class, already has is E02090.

See also

• E02010: duplicate property/field
• E02030: duplicate/ambiguous methods
• E02090: a listed trait is already a trait of another listed trait or of the super class

Examples

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

Fails with E02050: same trait referenced multiple times

#!ek9
defines module error.e02050.bad

  defines trait

    T1
      method1()
        <- rtn <- true

    T2
      method2()
        <- rtn <- true

    DuplicatedReferences1 with trait of T1, T2, T1
      method3()
        <- rtn <- true

    DuplicatedReferences2 with trait of error.e02050.bad::T1, T2, error.e02050.bad::T1
      method3()
        <- rtn <- true

    DuplicatedReferences3 with trait of error.e02050.bad::T1, T2, T1
      method3()
        <- rtn <- true

    DuplicatedReferences4 with trait of T1, T2, T1, T2, T1
      method3()
        <- rtn <- true

Fixed: Name each trait once in the 'with trait of' list

#!ek9
defines module error.e02050.good

  defines trait

    T1
      method1()
        <- rtn <- true

    T2
      method2()
        <- rtn <- true

    BothTraits with trait of T1, T2
      method3()
        <- rtn <- true

Questions and answers

These Q&A entries show E02050 and its fix:

• Q740: How does EK9 detect duplicate trait references and service path conflicts?