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TryCatch(3)	      User Contributed Perl Documentation	   TryCatch(3)

NAME
       TryCatch	- first	class try catch	semantics for Perl, without source
       filters.

DESCRIPTION
       This module aims	to provide a nicer syntax and method to	catch errors
       in Perl,	similar	to what	is found in other languages (such as Java,
       Python or C++).	The standard method of using "eval {}; if ($@) {}" is
       often prone to subtle bugs, primarily that its far too easy to stomp on
       the error in error handlers.  And also eval/if isn't the	nicest idiom.

SYNOPSIS
	use TryCatch;

	sub foo	{
	  my ($self) = @_;

	  try {
	    die	Some::Class->new(code => 404 ) if $self->not_found;
	    return "return value from foo";
	  }
	  catch	(Some::Class $e	where {	$_->code > 100 } ) {
	  }
	}

SYNTAX
       This module aims	to give	first class exception handling to perl via
       'try' and 'catch' keywords. The basic syntax this module	provides is
       "try { #	block }" followed by zero or more catch	blocks.	Each catch
       block has an optional type constraint on	it the resembles Perl6's
       method signatures.

       Also worth noting is that the error variable ($@) is localised to the
       try/catch blocks	and will not leak outside the scope, or	stomp on a
       previous	value of $@.

       The simplest case of a catch block is just

	catch {	... }

       where upon the error is available in the	standard $@ variable and no
       type checking is	performed. The exception can instead be	accessed via a
       named lexical variable by providing a simple signature to the catch
       block as	follows:

	catch ($err) { ... }

       Type checking of	the exception can be performed by specifing a type
       constraint or where clauses in the signature as follows:

	catch (TypeFoo $e) { ... }
	catch (Dict[code => Int, message => Str] $err) { ... }

       As shown	in the above example, complex Moose types can be used,
       including MooseX::Types style of	type constraints

       In addition to type checking via	Moose type constraints,	you can	also
       use where clauses to only match a certain sub-condition on an error.
       For example, assuming that "HTTPError" is a suitably defined TC:

	catch (HTTPError $e where { $_->code >=	400 && $_->code	<= 499 } ) {
	  return "4XX error";
	}
	catch (HTTPError $e) {
	  return "other	http code";
	}

       would return "4XX error"	in the case of a 404 error, and	"other http
       code" in	the case of a 302.

       In the case where multiple catch	blocks are present, the	first one that
       matches the type	constraints (if	any) will executed.

BENEFITS
       return. You can put a return in a try block, and	it would do the	right
       thing - namely return a value from the subroutine you are in, instead
       of just from the	eval block.

       Type Checking. This is nothing you couldn't do manually yourself, it
       does it for you using Moose type	constraints.

TODO
       o   Decide on "finally" semantics w.r.t return values.

       o   Write some more documentation

       o   Split out the dependancy on Moose

SEE ALSO
       MooseX::Types, Moose::Util::TypeConstraints, Parse::Method::Signatures.

AUTHOR
       Ash Berlin <ash@cpan.org>

THANKS
       Thanks to Matt S	Trout and Florian Ragwitz for work on Devel::Declare
       and various B::Hooks modules

       Vincent Pit for Scope::Upper that makes the return from block possible.

       Zefram for providing support and	XS guidance.

       Xavier Bergade for the impetus to finally fix this module in 5.12.

LICENSE
       Licensed	under the same terms as	Perl itself.

perl v5.24.1			  2013-03-22			   TryCatch(3)

NAME | DESCRIPTION | SYNOPSIS | SYNTAX | BENEFITS | TODO | SEE ALSO | AUTHOR | THANKS | LICENSE

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