Re: Bug with unset variables

[Roman Perepelitsa <roman.perepelitsa@xxxxxxxxx>]

On Thu, Nov 12, 2020 at 7:47 PM Felipe Contreras
<felipe.contreras@xxxxxxxxx> wrote:
>
> This is distinction without a difference, like saying we are not lost,
> we just don't know where we are. Conceptually it is the same thing,
> you are just using a different word for it. It's wordplay.
>
> An unset variable is for all intents and purposes a variable with a null value.

Only in languages where variables cannot have null values, and only
because you can declare "null" to be a synonym for "unset" in this
case.

> JavaScript

In JavaScript you unset a variable with `delete foo` and you assign it
a "null" value (in quotes because javascript has another null) with
`foo = undefined`. These are not equivalent.

Note that these two snippets have different effect:

  var foo

and

  var foo
  delete foo

Just line in zsh, and unlike ksh/bash.

> Python

Same thing but `del var` and `var = None`.

Et cetera. ksh and bash are rather exceptional in this regard.

Roman.