Does KSH_ARRAYS affect associative array semantics between zsh 5.8 and 5.9?

No, the KSH_ARRAYS option does not change the semantics of associative arrays between zsh 5.8 and 5.9. This option is specifically designed to toggle the indexing of numeric arrays from 1-based to 0-based. Since associative arrays use string-based keys, they remain fundamentally unaffected by this setopt.

The inconsistency you are observing when migrating from zsh 5.8 to 5.9 likely stems from how the shell handles the distinction between an unset key and a key assigned an empty string value, rather than the KSH_ARRAYS setting. In zsh 5.9, updates to the zsh/parameter module or parameter expansion optimizations may affect how empty values are reported in specific contexts, but the core logic for associative arrays remains stable.

To ensure consistent behavior across versions and regardless of active setopts, follow these practices:

n

• Use [[ -v ... ]] for existence: This operator checks if a variable or index is set, regardless of whether its value is empty. This is the most reliable way to verify if a key has been initialized.
• Avoid [[ -n ... ]] for existence: Using [[ -n ${assoc[key]} ]] checks if the value is non-empty. If the key exists but contains an empty string, this will return false, which often leads to perceived behavioral shifts.
• Explicit Initialization: Ensure keys are explicitly assigned assoc[key]="" if you need to track presence.

Verification Command:

Run the following snippet in both versions to verify the behavior:

typeset -A assoc
assoc[test]=""

if [[ -v assoc[test] ]]; then
    echo "Key exists"
else
    echo "Key does not exist"
fi

if [[ -n "${assoc[test]}" ]]; then
    echo "Value is not empty"
else
    echo "Value is empty"
fi

If you are still seeing inconsistent results with the -v check, please confirm if you are accessing the $parameters variable directly, as its expansion behavior is subject to version-specific internal module changes.