a=(outside)

f1() { readonly a=(1) ; }
f2() { readonly -a a=(2) ; }
f3() { readonly 'a=(3)' ; }
f4() { readonly -a 'a=(4)' ; }

f1
echo -n after f1:
declare -p a
f2
echo -n after f2:
declare -p a
f3
echo -n after f3:
declare -p a
f4
echo -n after f4:
declare -p a

b=(outside)
c=(outside)
d=(outside)

f2() { readonly -a b=(2) ; }
f3() { readonly 'c=(3)' ; }
f4() { readonly -a 'd=(4)' ; }

f2
echo -n after f2:
declare -p b
f3
echo -n after f3:
declare -p c
f4
echo -n after f4:
declare -p d

${THIS_SH} ./attr1.sub
${THIS_SH} ./attr2.sub