Re: equality as a variable

A. Sinan Unur <1usa@xxxxxxxxxxxxxxxxxxx> wrote in comp.lang.perl.misc:
> anno4000@xxxxxxxxxxxxxxxxxxxxxxx (Anno Siegel) wrote in
> news:dhjufn$801$1@xxxxxxxxxxxxxxxxxxxxxxxxx:
>
> > A. Sinan Unur <1usa@xxxxxxxxxxxxxxxxxxx> wrote in comp.lang.perl.misc:
> >> Brian Wakem <no@xxxxxxxxx> wrote in
> >> news:3q58ibFd6ikpU1@xxxxxxxxxxxxxx:
> >>
> >> > Shiraz wrote:
> >> >
> >> >> i need to put the equality in an if statement as a variable
> ...
>
> >> Hmmm ... Sorry, I am going to go with hash based solution:
>
> ...
>
> > I'd use the hash *and* eval:
> >
> > my %handlers = map { $_ => eval "sub { \$_[0] $_ \$_[ 1] }" }
> > qw( > < >= <= == != <=>),
> > # qw( gt lt ge le eq ne cmp),
> > ;
> >
> > That string-eval is perfectly safe, everything comes from inside the
> > source.
>
> I always type too much :))

It isn't just the laziness aspect, in fact the fewer lines of code may
take longer to write (and debug) than straight-forward typing of the
obvious. There is also reliability.

Basically, in the explicit definition of the hash you specify the same
thing twice which implies a possibility[1] of getting it wrong. Even
if the probability is minute, if you do this (programming) all day, it
is bound to happen once in a while, especially in maintenance. You're
safe from that when you specify each operator only once. The cost is
a possible loss in clarity.

Later you have more duplicate specifications:

# from memory
my %examples = (
'5 == 6' => [ 5, '==', 6],
'5 <= 6' => [ 5, '<=', 6],
# ...
);

In a similar vein, I wouldn't even use a hash for that, but specify a list
of strings:

my @examples = (
'5 == 5',
'5 <= 6',
'5 <=> 6',
'"E" eq "F"',
'"E" cmp "F"',
);

and run them as

print "$_: ", do_compare_op( split), "\n" for @examples;

with do_compare_op unchanged. That also shows them in the sequence
they are specified.

Anno

[1] initially mistyped "pissibility", was tempted to let it stand
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