Bug report: assigning $! to an array element doesn't work

[Frava <fravadona@xxxxxxxxx>]

Dear ZSH gurus,

I noticed the following problem with zsh 5.9 (macOS Sonoma, ARM M2) AND zsh 5.5.1 (Linux RHEL8 x86_64):

#!/bin/zsh

sleep 1 &

arr[1]=$!

typeset -p arr

output:

typeset -a arr=( '$!' )

The double-quoting doesn't work either:

#!/bin/zsh

sleep 1 &

arr[1]="$!"

errput:

unmatched "

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Thank you for your support,

Rafael.