/ 
Try-Chain-0.001
River stage zero No dependents
/ Try::Chain

NAME

Try::Chain - Call method, hash and/or array chains with break on undef

VERSION

0.001

SYNOPSIS

The module exports:

try       - imported from Try::Tiny
catch     - imported from Try::Tiny
finally   - imported from Try::Tiny
try_chain - implemented in this module
$call_m   - implemented in this module

Import what needed. The following code describes the full import:

use Try::Chain qw( try_chain finally try_chain $call_m );

EXAMPLE

Inside of this Distribution is a directory named example. Run this *.pl files.

DESCRIPTION

Call method, hash and/or array chains with break on undef means, that in some cases it is ok to get back nothing late or early.

Problem

In case of method chain like

my $scalar = $obj->foo(1)->bar(2)->baz(3);

my %hash = (
    any => 'any',
    baz => scalar $obj->foo(1)->bar(2)->baz(3),
);

and foo or bar can can return nothing or undef, you get an error: Can't call method ... on an undefined value.

A quick solution is:

my $scalar
    = $obj->foo(1)
    && $obj->foo(1)->bar(2)
    && $obj->foo(1)->bar(2)->baz(3);

my %hash = (
    any => 'any',
    baz => scalar $obj->foo(1)
           && $obj->foo(1)->bar(2)
           && $obj->foo(1)->bar(2)->baz(3),
);

In case of method foo and/or bar is performance critical code it is a bad idea to call the method code more then one time. The the solution looks like this:

my $foo    = $obj->foo(1);
my $bar    = $foo && $foo->bar(2);
my $scalar = $bar && $bar->baz(3);

my %hash = (
    any => 'any',
    baz => do {
        my $foo = $obj->foo(1);
        my $bar = $foo && $foo->bar(2);
        $bar && scalar $bar->baz(3);
    },
);

Solution

This module allows to call the chain by ignoring all undef errors in block:

my $scalar = try_chain { $obj->foo(1)->bar(2)->baz(3) };

my %hash = (
    any => 'any',
    baz => scalar try_chain { $obj->foo(1)->bar(2)->baz(3) },
);

Or better step by step?

my $scalar = $obj->$call_m('foo', 1)->$call_m('bar', 2)->$call_m('baz', 3);

my %hash = (
    any => 'any',
    baz => scalar $obj
        ->$call_m('foo', 1)
        ->$call_m('bar', 2)
        ->$call_m('baz', 3),
);

Also possible with maybe not existing hash or array references:

... = try_chain {
    no autovivication; # optional
    $any->foo->{key}->bar(@params)->[0]->baz
};

Full Try::Tiny support:

... = try_chain { ... } catch { ... } finally { ... };

Solution for the autovivification Problem

Switch off possible autovivication:

$result = try_chain {
    no autovivification;
    $any->foo->{key}->bar(@params)->[0]->baz;
};

@result = try_chain {
    no autovivification;
    $any->foo->{key}->bar(@params)->[0]->baz;
};

SUBROUTINES/METHODS

sub try_chain

Calls the whole try block breaks and ignores in undef.

sub $call_m

Calls the next method. For methods only.

DIAGNOSTICS

none

CONFIGURATION AND ENVIRONMENT

nothing

DEPENDENCIES

parent

Exporter

Try::Tiny

INCOMPATIBILITIES

not known

BUGS AND LIMITATIONS

none

SEE ALSO

Try::Tiny

autovivification

AUTHOR

Steffen Winkler

LICENSE AND COPYRIGHT

Copyright (c) 2017, Steffen Winkler <steffenw at cpan.org>. All rights reserved.

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