ksh93 style named references - semantics

references to references allowed, so:
  $ val=fred
  $ typeset -n ref=val
  $ typeset -n word=ref
  $ echo $word
  fred

can point to an unset variable:
  $ unset val
  $ typeset -n ref=val
  $ echo $ref

  $ echo $val

can point to array, assoc etc and will be treated as such:
  $ arr=(one two three)
  $ typeset -n val=arr
  $ echo ${val[1]}
  two

but cannot point to an array element:
  $ typeset -n val=arr[1]
  ksh: typeset: arr[1]: is not an identifier

also, the element of an array, assoc can not be a reference, just as it can't
be a float etc:
  $ typeset -n ref[1]=val
  ksh: typeset: ref: reference variable cannot be an array

but can't point to an invalid variable name:
  $ typeset -n ref=1val
  ksh: typeset: 1val: invalid variable name

or to nothing:
  $ typeset -n ref
  ksh: typeset: ref: no reference name
  $ typeset -n r=''
  ksh: typeset: : is not an identifier

or to a positional parameter

cycles and self-references blocked
  $ typeset -n ref=val
  $ typeset -n val=ref
  ksh: typeset: val: invalid self reference

references can't be exported
local applies to the reference not the variable

attributes apply to the value not the reference:
  $ typeset -n val=one
  $ typeset -n ref=val
  $ typeset -u ref
  $ echo $ref
  ONE
  $ echo $val
  ONE
this includes readonly

in ksh though:
  $ typeset -n -r ref=val
  ksh: typeset: ref: is read only
might be good if this would define ref as a readonly reference
  
dereference with ${!...}
  $ typeset -n ref=val
  $ echo ${!ref}
  val

dereference goes all the way so
  $ typeset -n ref=val
  $ typeset -n ref2=ref
  $ echo ${!ref2}
  val

ksh has compiled in alias - nameref='typeset -n'

typeset +n lists names of reference variables

typeset -n lists reference variables with values

only with -n will typeset act on the reference not the value

unset applies to the referenced variable

unset has a -n option which will unset the actual reference

typeset +n ref converts ref to a scalar

in ksh, references to positional variables are not allowed:
  $ typeset -n val=3
  ksh: typeset: 3: invalid variable name

if ksh is given an nameref as the index to a for loop it assigns the values as
for the reference, not the value. It could be very useful but isn't what what
you'd first expect. Is there a good alternative to avoid this:
  $ typeset -n ref=dummy
  $ for ref in var1 var2 ...

in ksh, typeset -n ref[one]=val is allowed with [one] ignored

reference records the local level so:
  $ function f {
  $   typeset -n ref=val
  $   typeset val=two
  $   echo $ref
  $ }
  $ val=one
  $ f val
would echo `one'

because of the above, it needs to handle the situation where
unset ref is done in the function above and also where ref is
then also reassigned a value.

ksh is not clever enough to allow typeset -n ref=ref in a function though

Extra issues in zsh:

local should be implied for typeset -n without +l.

what should ${(t)ref} return - the same as what it refers to with -nameref-
inserted?

should we use namerefs for prompt, rprompt, PROMPT-PROMPT4?

how messy will references to specials be?
might we need special references - I hope not.

any uses in completion functions? _call_function for starters.

test vared, read, case etc