Steffen Winkler
and 1 contributors

NAME

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

VERSION

0.005

SYNOPSIS

The module exports:

try

imported from Try::Tiny

catch

imported from Try::Tiny

finally

imported from Try::Tiny

try_chain

implemented here to call a complete chain or break

$call_m

implemented here to call a method or break

$call_em

implemented here to call an existing method or break

$fetch_i

implemented here to fetch an array index or break

$fetch_ei

implemented here to fetch an existing array index or break

$fetch_k

implemented here to fetch a hash key or break

$fetch_ek

implemented here to fetch an existing hash key or break

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

    use Try::Chain qw(
        try catch finally
        try_chain
        $call_m  $call_em
        $fetch_i $fetch_ei
        $fetch_k $fetch_ek
    );

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 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 { $any->foo->[0]->bar(@params)->{key}->baz };

Or better step by step?

    ... = $any
        ->$call_m('foo')
        ->$fetch_i(0)
        ->$call_m(bar => @params)
        ->$fetch_k('key')
        ->$call_m('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 undef errors.

sub $call_m

Calls the next method if possible.

sub $call_em

Calls the next method if possible and method exists.

sub $fetch_i

Calls the next index of an array reference if possible.

sub $fetch_ei

Calls the next index of an array reference if possible and index exists.

sub $fetch_k

Calls the next key of a hash reference if possible.

sub $fetch_ek

Calls the next key of a hash reference if possible and key exists.

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.