E07890: not mutable

What went wrong

You're attempting to modify an IMMUTABLE value. Once set, immutable values cannot be changed.

Worked examples

Compilable examples demonstrating this error and the correct fix:

• ek9 -q 141 (How does EK9 protect constants from mutation?)
• ek9 -q 143 (How do EK9 constants compare to const, final, and static ...)
• ek9 -q 140 (How do I define constants in EK9?)
• ek9 -q 142 (How do I use constants across modules in EK9?)

How to fix it

1. Use mutable variable if modification needed
2. Create new value instead of modifying
3. Remove mutation attempt

Common causes

• Trying to reassign const
• Mutation operation on immutable value

See also

• E07890: immutable value modification (this error)
• E08110: parameter reassignment

Examples

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

Fails with E07890: not mutable

#!ek9
defines module error.e07890.bad

  defines constant
    NAME <- "STEVE"
    START_DATE <- 2023-11-03

  defines function

    changeConstants()

      //A constant never changes
      START_DATE += P2D

      NAME: "Stephen"

Fixed: Copy the constant into a variable, and change that

#!ek9
defines module error.e07890.good

  defines constant
    NAME <- "STEVE"
    START_DATE <- 2023-11-03

  defines function

    nextWeek()
      <- rtn as Date: START_DATE

      //A variable, copied from the constant, can change
      rtn += P1W

    fullName()
      <- rtn as String: NAME + " Limb"

Questions and answers

These Q&A entries show E07890 and its fix:

• Q140: How do I define constants in EK9?
• Q141: How does EK9 protect constants from mutation?
• Q142: How do I use constants across modules in EK9?
• Q143: How do EK9 constants compare to const, final, and static in other languages?