Re: [HTCondor-users] class ad logic with undef (non-)equal

[Thomas Hartmann <thomas.hartmann@xxxxxxx>]

Hi TJ,

thanks for the explanation!
Then I will stick to
  regexp("strfoo", MyAdd ?: "" )
to avoid any undefined corners.

Cheers and thanks,
  Thomas


On 12/05/2021 16.13, John M Knoeller wrote:
> Yes, the ?: "operator" works when the first argument is a function, so
>
>  Â Âfn(x) ?: y
>
> will return the result of evaluating fn(x) if it isn't undefined and y 
> otherwise. But you need to write the expressions so that if f(x) is a 
> boolean then y is also a boolean. Âso this
>
>  Âregexp("strfoo",MyAdd) ?: ""
>
> Should probably be this instead
>
>  Âregexp("strfoo",MyAdd) ?: false
>
> Or you could put the ?: inside the function call to make sure that the 
> regular expression check never returns undefined
>
>  Âregexp("strfoo", MyAdd ?: "" )
>
> -tj
>
> ------------------------------------------------------------------------
> *From:* HTCondor-users <htcondor-users-bounces@xxxxxxxxxxx> on behalf of 
> Thomas Hartmann <thomas.hartmann@xxxxxxx>
> *Sent:* Wednesday, May 12, 2021 7:27 AM
> *To:* HTCondor-Users Mail List <htcondor-users@xxxxxxxxxxx>
> *Subject:* [HTCondor-users] class ad logic with undef (non-)equal
> Hi all,
>
> a short `undef` logic question:
>
> I wrote a statement like
>  ÂÂ ( Expr1 || regexp('strfoo',MyAdd) ) != true
>
> Unfortunately, I had assumed, that the regexp macro should always
> resolve to
>  ÂÂ ( Expr1 || true/false ) != true
> but Kruno pointed out, that in case the ad is undef the macro is not
> defined as well - which would result in
>  ÂÂ undef != true
> ð
>
>
> So, one question would be, if there is a `?`-like operator for a boolean
> non-equal comparison, that resolves in false when compared to undef?
>
>
> To catch undef cases, we are going now for
>  ÂÂ ( Expr1 || regexp('strfoo',MyAdd) ? : "" ) ) != true
> but we are not sure, if `?` as operator actually catches undefs here?
>
>
> Cheers,
>  ÂÂ Thomas
>
>
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