From: evanm@...
Date: 2004-06-23T02:49:26+09:00
Subject: Re: Cleaning up IO#popen

On Tue, Jun 22, 2004 at 08:32:06AM +0900, nobu.nokada@softhome.net wrote:
> You can give arguments as an Array. e.g.:
> 
>   IO.popen(%w[echo |arguments| contain shell's <meta> "chars"], "r")

Great, that's also a workable way.

> > it work? What is its args? Does it drop the '-' and mode arguments?
> 
> I'm not sure they are really evil.

Parsing a string for magic arguments moves logic from the code into the data.
It's poor design. Why not have a separate function with all the benefits that
brings? AFAIK there aren't any benefits in parsing magic values from a
string, but if you allow "-" then the programmer has to special case every
string he passes to verify that it's not "-" or risk running the wrong
function.

There are many more elegant ways of doing this, but the best is to not do it
at all.

> At Mon, 21 Jun 2004 06:06:02 +0900,
> evanm@frap.net wrote in [ruby-talk:104194]:
> > * takes a "mode string" arg for what really should be a separate function
> > * takes a "-" as a magic value for what really should be a separate function
> 
> Do you suggest to provide all possible combinations?

I suggest the code I submitted for IO.fork_open. There are only two
options, reading and writing, and this can be done in one with my
implementation of IO.fork_open which provides a bidirectional pipe.

IO.pread and IO.pwrite would be preferable to IO.popen with a mode argument,
IMHO.

Evan