Error - Error/exception handling in an OO-ish way
use Error qw(:try);
throw Error::Simple( "A simple error");
sub xyz {
...
record Error::Simple("A simple error")
and return;
}
unlink($file) or throw Error::Simple("$file: $!",$!);
try {
do_some_stuff();
die "error!" if $condition;
throw Error::Simple -text => "Oops!" if $other_condition;
}
catch Error::IO with {
my $E = shift;
print STDERR "File ", $E->{'-file'}, " had a problem\n";
}
except {
my $E = shift;
my $general_handler=sub {send_message $E->{-description}};
return {
UserException1 => $general_handler,
UserException2 => $general_handler
};
}
otherwise {
print STDERR "Well I don't know what to say\n";
}
finally {
close_the_garage_door_already(); # Should be reliable
}; # Don't forget the trailing ; or you might be surprised
The Error package provides two interfaces. Firstly Error provides
a procedural interface to exception handling. Secondly Error is a
base class for errors/exceptions that can either be thrown, for
subsequent catch, or can simply be recorded.
Errors in the class Error should not be thrown directly, but the
user should throw errors from a sub-class of Error.
Error exports subroutines to perform exception handling. These will
be exported if the :try tag is used in the use line.
try is the main subroutine called by the user. All other subroutines
exported are clauses to the try subroutine.
The BLOCK will be evaluated and, if no error is throw, try will return the result of the block.
CLAUSES are the subroutines below, which describe what to do in the
event of an error being thrown within BLOCK.
$err->isa(CLASS)
to be caught and handled by evaluating BLOCK.
BLOCK will be passed two arguments. The first will be the error
being thrown. The second is a reference to a scalar variable. If this
variable is set by the catch block then, on return from the catch
block, try will continue processing as if the catch block was never
found.
To propagate the error the catch block may call $err->throw
If the scalar reference by the second argument is not set, and the error is not thrown. Then the current try block will return with the result from the catch block.
try is looking for a handler, if an except clause is found
BLOCK is evaluated. The return value from this block should be a
HASHREF or a list of key-value pairs, where the keys are class names
and the values are CODE references for the handler of errors of that
type.
BLOCK
When evaluated BLOCK will be passed one argument, which will be the
error being processed.
Only one otherwise block may be specified per try block
BLOCK either after the code in the try block has
successfully completed, or if the try block throws an error then
BLOCK will be executed after the handler has completed.
If the handler throws an error then the error will be caught, the finally block will be executed and the error will be re-thrown.
Only one finally block may be specified per try block
The Error object is implemented as a HASH. This HASH is initialized
with the arguments that are passed to it's constructor. The elements
that are used by, or are retrievable by the Error class are listed
below, other classes may add to these.
-file
-line
-text
-value
-object
If -file or -line are not specified in the constructor arguments
then these will be initialized with the file name and line number where
the constructor was called from.
If the error is associated with an object then the object should be
passed as the -object argument. This will allow the Error package
to associate the error with the object.
The Error package remembers the last error created, and also the
last error associated with a package. This could either be the last
error created by a sub in that package, or the last error which passed
an object blessed into that package as the -object argument.
Error object and throw an error, which will be caught
by a surrounding try block, if there is one. Otherwise it will cause
the program to exit.
throw may also be called on an existing error to re-throw it.
Error object and returns it. This is defined for
syntactic sugar, eg
die with Some::Error ( ... );
Error object and returns it. This is defined for
syntactic sugar, eg
record Some::Error ( ... )
and return;
PACKAGE
$Error::Debug was non-zero when the error was
created, then stacktrace returns a string created by calling
Carp::longmess. If the variable was zero the stacktrace returns
the text of the error appended with the filename and line number of
where the error was created, providing the text does not end with a
newline.
text method, or it may append more
information. For example the file name and line number.
By default this method returns the -text argument that was passed to
the constructor, or the string "Died" if none was given.
$! at the
time.
By default this method returns the -value argument that was passed
to the constructor.
If the text value ends with at file line 1 as $@ strings do, then
this infomation will be used to set the -file and -line arguments
of the error object.
This class is used internally if an eval'd block die's with an error that is a plain string.
None, but that does not mean there are not any.
Graham Barr <gbarr@pobox.com>
The code that inspired me to write this was originally written by Peter Seibel <peter@weblogic.com> and adapted by Jesse Glick <jglick@sig.bsh.com>.
Arun Kumar U <u_arunkumar@yahoo.com>