/ 
Data-Decrement-0.001
River stage one • 2 direct dependents • 2 total dependents
/ Data::Decrement

NAME

Data::Decrement - Provide extra magic for auto-decrement

VERSION

This document describes version 0.001 of Data::Decrement (from Perl distribution Data-Decrement), released on 2019-01-25.

SYNOPSIS

To import the "decr" function that implements the logic of auto-decrement magic:

use Data::Decrement 'decr';

print decr("b00"); # prints "a99"

DESCRIPTION

Perl's auto-increment operator (++) has some convenience feature built in. Quoting perlop:

The auto-increment operator has a little extra builtin magic to it. If you
increment a variable that is numeric, or that has ever been used in a numeric
context, you get a normal increment. If, however, the variable has been used in
only string contexts since it was set, and has a value that is not the empty
string and matches the pattern "/^[a-zA-Z]*[0-9]*\z/", the increment is done as
a string, preserving each character within its range, with carry:

 print ++($foo = "99");      # prints "100"
 print ++($foo = "a0");      # prints "a1"
 print ++($foo = "Az");      # prints "Ba"
 print ++($foo = "zz");      # prints "aaa"

"undef" is always treated as numeric, and in particular is changed to 0 before
incrementing (so that a post-increment of an undef value will return 0 rather
than "undef").

The auto-decrement operator is not magical.

This module provides the counterpart for auto-decrement. Note that the decrement operation is not the exact reverse of auto-increment. In general, the rule is that decr($a++) will return the same value as the original $a before auto-increment, but when the carrying over to the leftmost character and it is already "A", "a", or "0", the original value is returned and a warning "Cannot decrement '<VALUE>'" is generated. Examples:

print decr(-123);            # prints "-124", treated as number
print decr(123);             # prints "122", treated as STRING
print decr(100);             # prints "099", treated as STRING
print decr(0);               # prints "0", warns "Cannot decrement '0'"
print decr("a1");            # prints "a0"
print decr("b0");            # prints "a9"
print decr("a0");            # prints "a0", warns "Cannot decrement 'a0'"
print decr("bZz0");          # prints "bZy9"
print decr("bZa0");          # prints "bYz9"
print decr("bAa0");          # prints "aZz9"
print decr("aAa0");          # prints "aAa0", warns "Cannot decrement 'aAa0'"

FUNCTIONS

decr

Usage:

decr($val) => $dec_val

Accept a value and return decremented value. If $val matches the pattern /^[a-zA-Z]*[0-9]*\z/, it will decremented as a string (note that positive integers match this pattern). Otherwise, it will be decremented numerically. undef is regarded as numeric 0.

Will emit a warning if cannot decrement a value.

HOMEPAGE

Please visit the project's homepage at https://metacpan.org/release/Data-Decrement.

SOURCE

Source repository is at https://github.com/perlancar/perl-Data-Decrement.

BUGS

Please report any bugs or feature requests on the bugtracker website https://rt.cpan.org/Public/Dist/Display.html?Name=Data-Decrement

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.

SEE ALSO

++ in perlop

dec-pl in App::IncrementUtils

AUTHOR

perlancar <perlancar@cpan.org>

COPYRIGHT AND LICENSE

This software is copyright (c) 2019 by perlancar@cpan.org.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.