NAME
   Exception::Class::TryCatch - Syntactic try/catch sugar for use with
   Exception::Class

VERSION
   version 1.13

SYNOPSIS
        use Exception::Class::TryCatch;

        # simple usage of catch()

        eval { Exception::Class::Base->throw('error') };
        catch my $err and warn $err->error;

        # catching only certain types or else rethrowing

        eval { Exception::Class::Base::SubClass->throw('error') };
        catch( my $err, ['Exception::Class::Base', 'Other::Exception'] )
            and warn $err->error;

        # catching and handling different types of errors

        eval { Exception::Class::Base->throw('error') };
        if ( catch my $err ) {
            $err->isa('this') and do { handle_this($err) };
            $err->isa('that') and do { handle_that($err) };
        }

        # use "try eval" to push exceptions onto a stack to catch later

        try eval {
            Exception::Class::Base->throw('error')
        };
        do {
            # cleanup that might use "try/catch" again
        };
        catch my $err; # catches a matching "try"

DESCRIPTION
   Exception::Class::TryCatch provides syntactic sugar for use with
   Exception::Class using the familiar keywords "try" and "catch". Its
   primary objective is to allow users to avoid dealing directly with $@ by
   ensuring that any exceptions caught in an "eval" are captured as
   Exception::Class objects, whether they were thrown objects to begin with
   or whether the error resulted from "die". This means that users may
   immediately use "isa" and various Exception::Class methods to process
   the exception.

   In addition, this module provides for a method to push errors onto a
   hidden error stack immediately after an "eval" so that cleanup code or
   other error handling may also call "eval" without the original error in
   $@ being lost.

   Inspiration for this module is due in part to Dave Rolsky's article
   "Exception Handling in Perl With Exception::Class" in *The Perl Journal*
   (Rolsky 2004).

   The "try/catch" syntax used in this module does not use code reference
   prototypes the way the Error.pm module does, but simply provides some
   helpful functionality when used in combination with "eval". As a result,
   it avoids the complexity and dangers involving nested closures and
   memory leaks inherent in Error.pm (Perrin 2003).

   Rolsky (2004) notes that these memory leaks may not occur in recent
   versions of Perl, but the approach used in Exception::Class::TryCatch
   should be safe for all versions of Perl as it leaves all code execution
   to the "eval" in the current scope, avoiding closures altogether.

USAGE
 "catch"
        # zero argument form
        my $err = catch;

        # one argument forms
        catch my $err;
        my $err = catch( [ 'Exception::Type', 'Exception::Other::Type' ] );

        # two argument form
        catch my $err, [ 'Exception::Type', 'Exception::Other::Type' ];

   Returns an "Exception::Class::Base" object (or an object which is a
   subclass of it) if an exception has been caught by "eval". If no
   exception was thrown, it returns "undef" in scalar context and an empty
   list in list context. The exception is either popped from a hidden error
   stack (see "try") or, if the stack is empty, taken from the current
   value of $@.

   If the exception is not an "Exception::Class::Base" object (or subclass
   object), an "Exception::Class::Base" object will be created using the
   string contents of the exception. This means that calls to "die" will be
   wrapped and may be treated as exception objects. Other objects caught
   will be stringified and wrapped likewise. Such wrapping will likely
   result in confusing stack traces and the like, so any methods other than
   "error" used on "Exception::Class::Base" objects caught should be used
   with caution.

   "catch" is prototyped to take up to two optional scalar arguments. The
   single argument form has two variations.

   *   If the argument is a reference to an array, any exception caught
       that is not of the same type (or a subtype) of one of the classes
       listed in the array will be rethrown.

   *   If the argument is not a reference to an array, "catch" will set the
       argument to the same value that is returned. This allows for the
       "catch my $err" idiom without parentheses.

   In the two-argument form, the first argument is set to the same value as
   is returned. The second argument must be an array reference and is
   handled the same as as for the single argument version with an array
   reference, as given above.

 "caught" (DEPRECATED)
   "caught" is a synonym for "catch" for syntactic convenience.

   NOTE: Exception::Class version 1.21 added a "caught" method of its own.
   It provides somewhat similar functionality to this subroutine, but with
   very different semantics. As this class is intended to work closely with
   Exception::Class, the existence of a subroutine and a method with the
   same name is liable to cause confusion and this method is deprecated and
   may be removed in future releases of Exception::Class::TryCatch.

   This method is no longer exported by default.

 "try"
        # void context
        try eval {
          # dangerous code
        };
        do {
          # cleanup code can use try/catch
        };
        catch my $err;

        # scalar context
        $rv = try eval { return $scalar };

        # list context
        @rv = try [ eval { return @array } ];

   Pushes the current error ($@) onto a hidden error stack for later use by
   "catch". "try" uses a prototype that expects a single scalar so that it
   can be used with eval without parentheses. As "eval { BLOCK }" is an
   argument to try, it will be evaluated just prior to "try", ensuring that
   "try" captures the correct error status. "try" does not itself handle
   any errors -- it merely records the results of "eval". "try { BLOCK }"
   will be interpreted as passing a hash reference and will (probably) not
   compile. (And if it does, it will result in very unexpected behavior.)

   Since "try" requires a single argument, "eval" will normally be called
   in scalar context. To use "eval" in list context with "try", put the
   call to "eval" in an anonymous array:

      @rv = try [ eval {return @array} ];

   When "try" is called in list context, if the argument to "try" is an
   array reference, "try" will dereference the array and return the
   resulting list.

   In scalar context, "try" passes through the scalar value returned by
   "eval" without modifications -- even if that is an array reference.

      $rv = try eval { return $scalar };
      $rv = try eval { return [ qw( anonymous array ) ] };

   Of course, if the eval throws an exception, "eval" and thus "try" will
   return undef.

   "try" must always be properly bracketed with a matching "catch" or
   unexpected behavior may result when "catch" pops the error off of the
   stack. "try" executes right after its "eval", so inconsistent usage of
   "try" like the following will work as expected:

        try eval {
            eval { die "inner" };
            catch my $inner_err
            die "outer" if $inner_err;
        };
        catch my $outer_err;
        # handle $outer_err;

   However, the following code is a problem:

        # BAD EXAMPLE
        try eval {
            try eval { die "inner" };
            die $@ if $@;
        };
        catch my $outer_err;
        # handle $outer_err;

   This code will appear to run correctly, but "catch" gets the exception
   from the inner "try", not the outer one, and there will still be an
   exception on the error stack which will be caught by the next "catch" in
   the program, causing unexpected (and likely hard to track) behavior.

   In short, if you use "try", you must have a matching "catch". The
   problem code above should be rewritten as:

        try eval {
            try eval { die "inner" };
            catch my $inner_err;
            $inner_err->rethrow if $inner_err;
        };
        catch my $outer_err;
        # handle $outer_err;

REFERENCES
   1.  perrin. (2003), "Re: Re2: Learning how to use the Error module by
       example", (perlmonks.org), Available:
       http://www.perlmonks.org/index.pl?node_id=278900 (Accessed September
       8, 2004).

   2.  Rolsky, D. (2004), "Exception Handling in Perl with
       Exception::Class", *The Perl Journal*, vol. 8, no. 7, pp. 9-13

SEE ALSO
   *   Exception::Class

   *   Error -- but see (Perrin 2003) before using

SUPPORT
 Bugs / Feature Requests
   Please report any bugs or feature requests through the issue tracker at
   <https://github.com/dagolden/Exception-Class-TryCatch/issues>. You will
   be notified automatically of any progress on your issue.

 Source Code
   This is open source software. The code repository is available for
   public review and contribution under the terms of the license.

   <https://github.com/dagolden/Exception-Class-TryCatch>

     git clone https://github.com/dagolden/Exception-Class-TryCatch.git

AUTHOR
   David Golden <[email protected]>

COPYRIGHT AND LICENSE
   This software is Copyright (c) 2014 by David Golden.

   This is free software, licensed under:

     The Apache License, Version 2.0, January 2004

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