Re: RFC: utils.pm

From: Ben Morrow (usenet_at_morrow.me.uk)
Date: 02/11/04 

Date: Wed, 11 Feb 2004 22:06:45 +0000 (UTC)

Tore Aursand <tore@aursand.no> wrote:
> On Wed, 11 Feb 2004 15:23:37 +0000, Ben Morrow wrote:
> >> split_csv( $value ) - Easy CSV splitting. (*)
>
> > As you say, there are modules to do this. Or
> >
> > @values = split /,/, $values;
>
> Not quite as powerful as this one;
>
> my @array = ();
> push( @array, $+ ) while $string =~ m{
> "([^\"\\]*(?:\\.[^\"\\]*)*)",? # groups the phrase inside the quotes
            ^ ^
            Unnecessary

> | ([^,]+),?
> | ,
> }gx;
> push( @array, undef ) if ( substr($string, -1, 1) eq ',' );

use Text::Balanced qw/extract_multiple extract_delimited/;

extract_multiple $string,
    [ sub { extract_delimited $_[0], '"' }, qr/[^,]*/ ],
    undef, 1;

Or, there are modules to do it.

> >> random_string( $length ) - Generates a random string $length
> >> characters long.
>
> > This is a little harder... also *much* less useful.
>
> Maybe, but I find myself constantly using this one when I want to create
> cookies. Nice to have. :)

Well, yeah; but hardly of general utility. Perl != CGI.

> >> as_string( $value, [$default] ) - Always returns a defined value,
> >> optionally $default if $value
> >> isn't defined.
>
> > Eh what? You don't *need* to cast in Perl.
> >
> > $value || $default
>
> This only returns $default if $value isn't true. So if we have this
> function:

Yeah, yeah; I know that. It's good enough most of the time,
though. Roll on 5.10 when (I think) they're going to put // in (which
tests for definedness rather than truth).

> > or defined($value) ? $value : $default
>
> Better, but I'm tired to writing this god damn line each time I want to
> make sure that a value is defined. :)

But it's a lot clearer... if the default is not supplied, your
function is a noop; otherwise, it is a defined-or-default
function. Not what I'd call as_string.

> When it comes to "casting". Maybe it's not the correct word to use, but
> when dealing with ie. CGI parameters, I find my functions useful. Here's
> an example;
>
> my $firstname = as_string( $cgi->param('firstname') );

What, precisely, is the difference between this and

    my $firstname = $cgi->param('firstname');

?

> >> as_int( $value ) - Always returns $value as an integer.
>
> > err.. int($value)
>
> What if $value isn't a number? Ah. A warning occurs, of course. I don't
> want warnings.

So turn it off. Not exactly hard. And, again, an explicit statement to
a reader of your code that you are prepared to tolerate non-numeric
inputs.

> >> as_decimal( $value, [$decimals] ) - Always returns $value as a
> >> decimal number with $decimals
> >> numbers after the decimal point.
>
> > sprintf
>
> Excactly what 'as_decimal' uses, except that I prefer writing
>
> my $value = as_decimal( 1.23456789, 2 );
>
> instead of
>
> my $value = sprintf( '%.2f', 1.23456789 );

Why? This slightly peculiar taste of yours hardly justifies inclusion
in a core module.

> >> as_boolean( $value ) - Always returns $value as a boolena value (ie.
> >> TRUE/1 or FALSE/0).
>
> > !!$value
>
> Yeah, but 'as_boolean' takes care of "other" boolean values to;
>
> sub as_boolean {
> my $value = as_string( shift );
> return ( $value =~ m,^1|y|yes|on|true$,i ) ? 1 : 0;
> }

Whoa... not what it said on the tin *at* *all*. I'd definitely much
prefer that to be explicit in the code; and you *really* don't need
that ?:: m// already returns a boolean value...

> >> as_date( $value ) - Always returns $value as a date (YYYY-MM-DD).
> >> as_time( $value ) - Always returns $value as a time (HH:MM:SS).
> >> as_datetime( $value ) - Always returns $value as a datetime (which
> >> means combining as_date() and as_time()).
>
> > POSIX::strftime
>
> 'as_date', 'as_time' and 'as_datetime' are - of course - a lot easier to
> use than 'strftime'. :)

'Of course'? I think not. Apart from anything else, it is clear from a
strftime call what format the result will be in, whereas your
functions are not.

> >> VALIDATION
> >> Each of the CASTING functions also have a is_* function, which returns
> >> TRUE/1 or FALSE/0 depending on wether the input argument conforms to
> >> the datatype.
>
> > Ummm... everything is (can be) a string.
>
> Yes, but not everything can be everything _else_ than a string. Let's
> look at my CGI parameter example again. Instead of writing
>
> my $nr = (defined $cgi->param('nr')) ? $cgi->param('nr') : 0;
> unless ( $nr >= 0 && $nr <= 12 ) {
> # Error
> }
>
> I want to write
>
> my $nr = as_int( $cgi->param('nr') );
> unless ( is_int($nr, 0, 12) ) {
> # Error
> }

I wasn't debating is_int, but is_string. What, in fact, does this
function *do*?

> > is_int is simply $value =~ /^\d+$/.
>
> No. Take a look at this:
>
> my @values = ( 2, -2, +2, '2', '-2', '+2' );
> foreach ( @values ) {
> print "Is $_ an integer? ";
> ( /^\d+$/ ) ? print 'Yes' : print 'No';
> print "\n";
> }

OK, my mistake... $value =~ /^[+-]?\d+$/.

> > Dates can and should be handled by your favourite date-time parsing
> > module: the code is non-trivial, so should be reused.
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> I guess you're right. I created many of them (the functions) "by hand",
> though, and tested them agains Date::Calc and Date::Manip. Man, that was
> one useful learning session. :)

Right, it's a good way to learn... but in production, use the
peer-reviewed code. *That's what it's there for*.

> > I can't think offhand how I'd do is_decimal, probably because I've
> > never had occasion to.
>
> I once (...) encountered a problem with a web form where the user had to
> register some data, and he/she _had_ to enter a number as a decimal. That
> was to make sure that the data entered was as accurate as possible, or
> something like that;
>
> sub is_decimal {
> my $value = as_string( shift );
> return ( $value =~ m,^[-+]?(\d+)?\.\d+$, ) ? 1 : 0;
                                   ^^^^^^
                                    \d*
> }

Right. Once. As I said.

> >> random_number( $min, $max ) - Returns a random number in the range
> >> $min to $max.
>
> > (rand * ($max - $min)) + $min
>
> Right, but what if only one of $min or $max is known?

Err... what if? What do you *want* to happen in that case? (And how do
you implement it?... insofaras I am aware, the random-number generator
will not accept 'infinity' as an argument.)

> >> format_number( $value, $separator ) - Formats a number with a given
> >> separator; 1234 becomes 1,234.
>
> > Less trivial... is probably better done by something locale-aware.
>
> Who says that a 'Utils' module can't be locale-aware? :)

OK; but personally I'd rather that sprintf be made aware of the '
modifier from SUSv2 (which does just this).

> >> unique( $arrayref ) - Returns only the unique elements in $array.
> >> intersection( $arrayref1, $arrayref2 ) - Computes the intersection
> >> of two array references.
> >> union( $arrayref1, $arrayref2 ) - Computes the union of two array
> >> references.
>
> > These should all be in a module called Set::Util... feel free to write
> > it.
>
> It isn't in a module already? Doesn't it fit into List::Util?

Well, maybe, but they aren't in there. Personally, I'd have said
there's a useful distinction to be made between 'operations on ordered
sets of data' (List::Util) and 'operations on unordered sets of data'
(Set::Util).

Anyway, if you thought it was in a module already *why aren't you
using it*?

Ben 

-- 
   If you put all the prophets,   |   You'd have so much more reason
   Mystics and saints             |   Than ever was born
   In one room together,          |   Out of all of the conflicts of time.
ben@morrow.me.uk |----------------+---------------| The Levellers, 'Believers'

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