Subset::Helper - create awesome subsets
SYNOPSIS
use Subset::Helper;
subset Positive of Int
where subset-is * > 0, 'Value must be above zero';
my Positive $x = 42; # success
my Positive $x = -2; # Fails with 'Value must be above zero';
DESCRIPTION
This module solves two inconveniences with Perl 6's subsets:
1) Display of useful error messages when type check fails
2) Avoid evaluating subset's condition for `Any` values,
which is what happens with optional parameters
EXPORTED SUBROUTINES
subset-is
subset Positive of Int where subset-is * > 0;
subset RoverCam of Str where subset-is
{ $_ ∈ set <MAST CHEMCAM FHAZ RHAZ> },
'Valid cameras are MAST, CHEMCAM, FHAZ, and RHAZ';
Takes one mandatory positional argument, which is the
code to execute to check the validity of value, and an
optional descriptive error message to show when the value
doesn't match the subset.
Note: undefined values are accepted by the subset.
This exists to make it possible to cleanly define subsets
for optional parameters, for which the type check is still
called, even when they aren't provided in the sub/method calls.
CONFUSING ERRORS
You can't declare our scoped subsets within roles. If you're
using this module, however, that error will instead point
to the end of the declaration, saying expecting any of: postfix.
Simply prefix your subset with my
BUGS AND LIMITATIONS
Rakudo may evaluate whether a value matches the subset TWICE:
once to check the match and once to get sensible error information.
Thus, currently the error message you provide is printed twice.
Patches to fix this are welcome.
REPOSITORY
Fork this module on GitHub:
https://github.com/raku-community-modules/Subset-Helper
BUGS
To report bugs or request features, please use
https://github.com/raku-community-modules/Subset-Helper/issues
AUTHOR
Zoffix Znet (http://zoffix.com/)
LICENSE
You can use and distribute this module under the terms of the
The Artistic License 2.0. See the LICENSE file included in this
distribution for complete details.