=head1 SYNOPSIS
# Assertations are on.
use Carp::Assert;
assert(1 == 1) if DEBUG;
# Assertations are off.
use Carp::Assert qw(:NDEBUG);
assert(1 == 1) if DEBUG;
=head1 DESCRIPTION
"We are ready for any unforseen event that may or may not
occur."
- Dan Quayle
Carp::Assert is intended for a purpose like the ANSI C library assert.h.
If you're already familiar with assert.h, then you can probably skip this and
go straight to the FUNCTIONS section.
Assertations are the explict expressions of your assumptions about the reality
your program is expected to deal with, and a declaration of those which it is
not. They are used to prevent your program from blissfully processing garbage
inputs (garbage in, garbage out becomes garbage in, error out) and to tell you
when you've produced garbage output. (If I was going to be a cynic about Perl
and the user nature, I'd say there are no user inputs but garbage, and Perl
produces nothing but...)
An assertation is used to prevent the impossible from being asked of your
code, or at least tell you when it does. For example:
# Take the square root of a number.
sub my_sqrt {
my($num) = shift;
# the square root of a negative number is imaginary.
assert($num >= 0);
return sqrt $num;
}
The assertation will warn you if a negative number was handed to your
subroutine, a reality the routine has no intention of dealing with.
An assertation should also be used a something of a reality check, to make
sure what your code just did really did happen:
open(FILE, $filename) || die $!;
@stuff = <FILE>;
@stuff = do_something(@stuff);
# I should have some stuff.
assert(scalar(@stuff) > 0);
The assertation makes sure you have some @stuff at the end. Maybe the file
was empty, maybe do_something() returned an empty list... either way, the
assert() will give you a clue as to where the problem lies, rather than 50
lines down when you print out @stuff and discover it to be empty.
Since assertations are designed for debugging and will remove themelves from
production code, your assertations should be carefully crafted so as to not
have any side-effects, change any variables or otherwise have any effect on
your program. Here is an example of a bad assertation:
assert($error = 1 if $king ne 'Henry'); # bad!
It sets an error flag which may then be used somewhere else in your program.
When you shut off your assertations with the $DEBUG flag, $error will no
longer be set.
=head1 AUTHOR
Michael G Schwern <
[email protected]>
WHAT IS THIS?
This is Carp::Assert, a perl module. Please see the README that comes with
this distribution.
HOW DO I INSTALL IT?
To install this module, cd to the directory that contains this README
file and type the following:
perl Makefile.PL
make
make test
make install
To install this module into a specific directory, do:
perl Makefile.PL PREFIX=/name/of/the/directory
...the rest is the same...
Please also read the perlmodinstall man page, if available.
WHAT MODULES DO I NEED?
Carp
