* Documenting $(( foo )) as similar to $(( ($foo) ))
[not found] ` <CAHYJk3SWzLZnzaHvt109Go46G8LQ0Qb1QBQR8CDn5mbDQGVhdA@mail.gmail.com>
@ 2024-02-16 5:45 ` Lawrence Velázquez
2024-02-16 17:40 ` Bart Schaefer
0 siblings, 1 reply; 2+ messages in thread
From: Lawrence Velázquez @ 2024-02-16 5:45 UTC (permalink / raw)
To: Mikael Magnusson, Bart Schaefer; +Cc: zsh-workers
On Sun, Feb 4, 2024, at 9:43 PM, Mikael Magnusson wrote:
> On 2/5/24, Bart Schaefer <schaefer@brasslantern.com> wrote:
>> On Sun, Feb 4, 2024 at 12:49 PM Lawrence Velázquez <larryv@zsh.org> wrote:
>>>
>>> I'm not sure if the zsh manual spells this behavior out explicitly,
>>> but bash and ksh share it.
>>
>> "Arithmetic Evaluation" says (pretty far down after the discussion of
>> operators):
>> ===
>> Named parameters and subscripted arrays can be referenced by name within
>> an arithmetic expression without using the parameter expansion syntax.
>> For example,
>> ((val2 = val1 * 2))
>> assigns twice the value of $val1 to the parameter named val2.
>>
>> =(and later)=
>>
>> Scalar variables can hold integer or floating point values at different
>> times; there is no memory of the numeric type in this case.
>>
>> If a variable is first assigned in a numeric context without previously
>> being declared, it will be implicitly typed as integer or float and
>> retain that type either until the type is explicitly changed or until
>> the end of the scope. This can have unforeseen consequences.
>> ===
>>
>> It doesn't explicitly say how "the value of $val1" is determined, but
>> if it were expanded with $val1 you'd get the whole text string which
>> would then be interpreted as arithmetic, so expanding without the $
>> works the same.
>
> This last bit is not 100% true, a parameter will combine into its
> context with $ but not without:
> % a=3+2
> % echo $(( 5 / a )) # 5/5
> 1
> % echo $(( 5 / $a )) # 5/3 + 2
> 3
>
> I think effectively you can think of foo as ($foo), at least in all
> cases I can think of to try.
I just noticed that Bart added the following text to zshmisc(1):
If the expansion of $val1 is text rather than a number,
then when val1 is referenced that text is itself evaluated
as a math expression as if surrounded by parentheses
`($val1)'.
I assumed that Mikael's comparison of foo with ($foo) was meant to
be an analogy, so I didn't nitpick it at the time, but I worry that
this addition to the documentation could be misconstrued as implying
that code like this ought to be valid:
% foo='1) + (2'
% print $((foo))
zsh: bad math expression: unexpected ')'
...just because this is valid (if ill-advised):
% print $((($foo)))
3
--
vq
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Documenting $(( foo )) as similar to $(( ($foo) ))
2024-02-16 5:45 ` Documenting $(( foo )) as similar to $(( ($foo) )) Lawrence Velázquez
@ 2024-02-16 17:40 ` Bart Schaefer
0 siblings, 0 replies; 2+ messages in thread
From: Bart Schaefer @ 2024-02-16 17:40 UTC (permalink / raw)
To: Zsh hackers list
On Thu, Feb 15, 2024 at 9:46 PM Lawrence Velázquez <larryv@zsh.org> wrote:
>
> I just noticed that Bart added the following text to zshmisc(1):
>
> If the expansion of $val1 is text rather than a number,
> then when val1 is referenced that text is itself evaluated
> as a math expression as if surrounded by parentheses
> `($val1)'.
>
> I assumed that Mikael's comparison of foo with ($foo) was meant to
> be an analogy, so I didn't nitpick it at the time, but I worry that
> this addition to the documentation could be misconstrued
It was my hope/expectation that "as if" would be adequate there. Note
that in that paragraph we're talking about how val1 works WITHOUT a $
prefix whereas here here you have it WITH a $ prefix:
> ...just because this is valid (if ill-advised):
>
> % print $((($foo)))
> 3
The latter is only "valid" because of order-of-operations effects, the
inner $foo is expanded before the outer $(( )).
If you can suggest a better way to express "expansion of $val1 is
text" please do. I rejected "the value of val1" because prior
sentences already refer to "the value" as the result after arithmetic
occurs whereas here we want to refer to the string before arithmetic.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2024-02-16 5:45 ` Documenting $(( foo )) as similar to $(( ($foo) )) Lawrence Velázquez
2024-02-16 17:40 ` Bart Schaefer
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