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Tomas Pokorny > Syntax-Feature-Try > Syntax::Feature::Try



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Module Version: 1.005   Source  


Syntax::Feature::Try - try/catch/finally statement for exception handling


    use syntax 'try';

    try {
        # run this code and handle errors
    catch (My::Class::Err $e) {
        # handle exception based on class "My::Class::Err"
    catch ($e) {
        # handle other exceptions
    finally {
        # cleanup block


This module implements syntax for try/catch/finally statement with behaviour similar to other programming languages (like Java, Python, etc.).

It handles correctly return/wantarray inside try/catch/finally blocks.

It uses perl keyword/parser API. So it requires perl >= 5.14.



To initialize this syntax feature call:

    use syntax 'try';


The try block is executed. If it throws an error, then first catch block (in order) that can handle thrown error will be executed. Other catch blocks will be skipped.

If none of catch blocks can handle the error, it is thrown out of whole statement. If try block does not throw an error, all catch blocks are skipped.

catch error class

    catch (My::Error $err) { ... }

This catch block can handle error that is instance of class My::Error or any of it's subclasses.

Caught error is accessible inside catch block via declared local variable $err.

catch all errors

To catch all errors use syntax:

    catch ($e) { ... }

Caught error is accessible inside catch block via declared local variable $e.

catch without variable

Variable name in catch block is not mandatory:

    try {
    catch (MyError::FileNotFound) {
        print "file not found";
    catch {
        print "operation failed";

rethrow error

To rethrow caught error call "die $err".

For example (log any Connection::Error):

    try { ... }
    catch (Connection::Error $err) {
        die $err;


The finally block is executed at the end of statement. It is always executed (even if try or catch block throw an error).

    my $fh;
    try {
        $fh = IO::File->new("/etc/hosts");
    finally {
        $fh->close if $fh;

WARNING: If finally block throws an exception, originaly thrown exception (from try/catch block) is discarded. You can convert errors inside finally block to warnings:

    try {
        # try block
    finally {
        try {
            # cleanup code
        catch ($e) { warn $e }

Supported features ^


This module is compatible with Exception::Class

    use Exception::Class (
    use syntax 'try';

    try {
        My::Test::Error->throw('invalid password');
    catch (My::Test::Error $err) {
        # handle error here


This module is able to handle subtypes defined using Moose::Util::TypeConstraints (but it does not require to be this package installed if you don't use this feature).

    use Moose::Util::TypeConstraints;

    class_type 'Error' => { class => 'My::Error' };
    subtype 'BillingError', as 'Error', where { $_->category eq 'billing' };

    try {
    catch (BillingError $err) {
        # handle subtype BillingError

return from subroutine

This module supports calling "return" inside try/catch/finally blocks to return values from subroutine.

    sub read_config {
        my $file;
        try {
            $fh = IO::File->new(...);
            return $fh->getline; # it returns value from subroutine "read_config"
        catch ($e) {
            # log error
        finally {
            $fh->close() if $fh;

using custom exception class matcher

There is possible register own subroutine (custom exception matcher) for extending internal className-matcher logic.

For example:

    use syntax 'try';

    sub is_expected_ref {
        my ($exception, $className) = @_;
        my ($expected_ref) = $className =~ /^is_ref::(.+)/;

        # use default logic if $className is not begning with 'is_ref::'
        return if not $expected_ref;

        return ( ref($exception) eq $expected_ref ? 1 : 0 );



    try { ... }
    catch (is_ref::CODE) {
        # there is handled any exception that is CODE-reference,
        # because custom exception matcher returns 1 in this case

Exception matcher subroutine has two arguments: first ($exception) is tested exception, second ($className) is className expected in "catch block". It should return undef if given $className cannon be handled by exception matcher (in this case next registered matchers or default matcher is executed) otherwise return 1 or 0 as result of your own match $exception to $className.

Note that multiple custom matchers may be registered.



@_ is not accessible inside try/catch/finally blocks, because these blocks are internally called in different context.

next, last, redo

next, last and redo is not working inside try/catch/finally blocks, because these blocks are internally called in different context.


goto can't be used to get out of a try, catch or finally block.


None bugs known.


syntax - Active syntax extensions

Exception::Class - A module that allows you to declare real exception classes in Perl


Other similar packages






Tomas Pokorny <tnt at cpan dot org>


Copyright 2013 - Tomas Pokorny.

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

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