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From: Janis Papanagnou <janis_papanagnou+ng@hotmail.com>
Newsgroups: comp.unix.shell
Subject: Re: [ksh93u+m] Performance warning message
Date: Mon, 28 Oct 2024 01:21:17 +0100
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On 25.10.2024 06:46, Janis Papanagnou wrote:
> For this command
> 
>   typeset -i indents=$(( level * indent_factor ))    ###
> 
> with two integer variables, 'level' and 'indent_factor', declared
> I'm getting this nice warning message
> 
>   warning: line 28: indents=$(( level * indent_factor ))
>       is slower than ((indents= level * indent_factor ))
> 
> I thought (to avoid the warning) I'd have to split the lines like
> 
>   typeset -i indents
>   (( indents = level * indent_factor ))
> 
> but I noticed that we can also write
> 
>   (( typeset -i indents = level * indent_factor ))
> 
> (I wasn't aware about the 'typeset' command possible in arithmetic
> expressions.)

Oops! - That's wrong. - I had just tested that only with 'ksh -n'.

ksh -n  had produced the above performance warning message, but it
did not produce an error message for the (( typeset ... )) syntax,
which I saw just now when invoking the shell regularly on the code.

This is really odd (shell-)behavior! (Reporting a warning but not
an error.) - Looks like a bug to me.[*]

So we have to either use the "non-performant" syntax marked '###'
or separate the statements on two lines.

> 
> Though I wonder why Ksh doesn't silently optimize the '###' marked
> code since Ksh optimizes so many less obvious and much more complex
> things.
> 
> Janis

[*] The man page says for option '-n':
    "Read commands and check them for syntax errors, [...]"
So the warning message is just an undocumented feature for free?
And the 'typeset' inside the arithmetic command is syntactically
okay and deserves no diagnostic message?