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.\" ========================================================================
.\"
.IX Title "autodie::exception 3perl"
.TH autodie::exception 3perl 2024-01-12 "perl v5.38.2" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH NAME
autodie::exception \- Exceptions from autodying functions.
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 2
\&    eval {
\&        use autodie;
\&
\&        open(my $fh, \*(Aq<\*(Aq, \*(Aqsome_file.txt\*(Aq);
\&
\&        ...
\&    };
\&
\&    if (my $E = $@) {
\&        say "Ooops!  ",$E\->caller," had problems: $@";
\&    }
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
When an autodie enabled function fails, it generates an
\&\f(CW\*(C`autodie::exception\*(C'\fR object.  This can be interrogated to
determine further information about the error that occurred.
.PP
This document is broken into two sections; those methods that
are most useful to the end-developer, and those methods for
anyone wishing to subclass or get very familiar with
\&\f(CW\*(C`autodie::exception\*(C'\fR.
.SS "Common Methods"
.IX Subsection "Common Methods"
These methods are intended to be used in the everyday dealing
of exceptions.
.PP
The following assume that the error has been copied into
a separate scalar:
.PP
.Vb 3
\&    if ($E = $@) {
\&        ...
\&    }
.Ve
.PP
This is not required, but is recommended in case any code
is called which may reset or alter \f(CW$@\fR.
.PP
\fIargs\fR
.IX Subsection "args"
.PP
.Vb 1
\&    my $array_ref = $E\->args;
.Ve
.PP
Provides a reference to the arguments passed to the subroutine
that died.
.PP
\fIfunction\fR
.IX Subsection "function"
.PP
.Vb 1
\&    my $sub = $E\->function;
.Ve
.PP
The subroutine (including package) that threw the exception.
.PP
\fIfile\fR
.IX Subsection "file"
.PP
.Vb 1
\&    my $file = $E\->file;
.Ve
.PP
The file in which the error occurred (eg, \f(CW\*(C`myscript.pl\*(C'\fR or
\&\f(CW\*(C`MyTest.pm\*(C'\fR).
.PP
\fIpackage\fR
.IX Subsection "package"
.PP
.Vb 1
\&    my $package = $E\->package;
.Ve
.PP
The package from which the exceptional subroutine was called.
.PP
\fIcaller\fR
.IX Subsection "caller"
.PP
.Vb 1
\&    my $caller = $E\->caller;
.Ve
.PP
The subroutine that \fIcalled\fR the exceptional code.
.PP
\fIline\fR
.IX Subsection "line"
.PP
.Vb 1
\&    my $line = $E\->line;
.Ve
.PP
The line in \f(CW\*(C`$E\->file\*(C'\fR where the exceptional code was called.
.PP
\fIcontext\fR
.IX Subsection "context"
.PP
.Vb 1
\&    my $context = $E\->context;
.Ve
.PP
The context in which the subroutine was called by autodie; usually
the same as the context in which you called the autodying subroutine.
This can be 'list', 'scalar', or undefined (unknown).  It will never
be 'void', as \f(CW\*(C`autodie\*(C'\fR always captures the return value in one way
or another.
.PP
For some core functions that always return a scalar value regardless
of their context (eg, \f(CW\*(C`chown\*(C'\fR), this may be 'scalar', even if you
used a list context.
.PP
\fIreturn\fR
.IX Subsection "return"
.PP
.Vb 1
\&    my $return_value = $E\->return;
.Ve
.PP
The value(s) returned by the failed subroutine.  When the subroutine
was called in a list context, this will always be a reference to an
array containing the results.  When the subroutine was called in
a scalar context, this will be the actual scalar returned.
.PP
\fIerrno\fR
.IX Subsection "errno"
.PP
.Vb 1
\&    my $errno = $E\->errno;
.Ve
.PP
The value of \f(CW$!\fR at the time when the exception occurred.
.PP
\&\fBNOTE\fR: This method will leave the main \f(CW\*(C`autodie::exception\*(C'\fR class
and become part of a role in the future.  You should only call
\&\f(CW\*(C`errno\*(C'\fR for exceptions where \f(CW$!\fR would reasonably have been
set on failure.
.PP
\fIeval_error\fR
.IX Subsection "eval_error"
.PP
.Vb 1
\&    my $old_eval_error = $E\->eval_error;
.Ve
.PP
The contents of \f(CW$@\fR immediately after autodie triggered an
exception.  This may be useful when dealing with modules such
as Text::Balanced that set (but do not throw) \f(CW$@\fR on error.
.PP
\fImatches\fR
.IX Subsection "matches"
.PP
.Vb 1
\&    if ( $e\->matches(\*(Aqopen\*(Aq) ) { ... }
\&
\&    if ( \*(Aqopen\*(Aq ~~ $e ) { ... }
.Ve
.PP
\&\f(CW\*(C`matches\*(C'\fR is used to determine whether a
given exception matches a particular role.
.PP
An exception is considered to match a string if:
.IP \(bu 4
For a string not starting with a colon, the string exactly matches the
package and subroutine that threw the exception.  For example,
\&\f(CW\*(C`MyModule::log\*(C'\fR.  If the string does not contain a package name,
\&\f(CW\*(C`CORE::\*(C'\fR is assumed.
.IP \(bu 4
For a string that does start with a colon, if the subroutine
throwing the exception \fIdoes\fR that behaviour.  For example, the
\&\f(CW\*(C`CORE::open\*(C'\fR subroutine does \f(CW\*(C`:file\*(C'\fR, \f(CW\*(C`:io\*(C'\fR and \f(CW\*(C`:all\*(C'\fR.
.Sp
See "CATEGORIES" in autodie for further information.
.Sp
On Perl 5.10 and above, using smart-match (\f(CW\*(C`~~\*(C'\fR) with an
\&\f(CW\*(C`autodie::exception\*(C'\fR object will use \f(CW\*(C`matches\*(C'\fR underneath.  This module
used to recommend using smart-match with the exception object on the left
hand side, but in future Perls that is likely to stop working.
The smart-match facility of this class should only be used with the
exception object on the right hand side.  Having the exception object on
the right is both future-proof and portable to older Perls, back to 5.10.
Beware that this facility can only
be relied upon when it is certain that the exception object actually is
an \f(CW\*(C`autodie::exception\*(C'\fR object; it is no more capable than an explicit
call to the \f(CW\*(C`matches\*(C'\fR method.
.SS "Advanced methods"
.IX Subsection "Advanced methods"
The following methods, while usable from anywhere, are primarily
intended for developers wishing to subclass \f(CW\*(C`autodie::exception\*(C'\fR,
write code that registers custom error messages, or otherwise
work closely with the \f(CW\*(C`autodie::exception\*(C'\fR model.
.PP
\fIregister\fR
.IX Subsection "register"
.PP
.Vb 1
\&    autodie::exception\->register( \*(AqCORE::open\*(Aq => \e&mysub );
.Ve
.PP
The \f(CW\*(C`register\*(C'\fR method allows for the registration of a message
handler for a given subroutine.  The full subroutine name including
the package should be used.
.PP
Registered message handlers will receive the \f(CW\*(C`autodie::exception\*(C'\fR
object as the first parameter.
.PP
\fIadd_file_and_line\fR
.IX Subsection "add_file_and_line"
.PP
.Vb 1
\&    say "Problem occurred",$@\->add_file_and_line;
.Ve
.PP
Returns the string \f(CW\*(C` at %s line %d\*(C'\fR, where \f(CW%s\fR is replaced with
the filename, and \f(CW%d\fR is replaced with the line number.
.PP
Primarily intended for use by format handlers.
.PP
\fIstringify\fR
.IX Subsection "stringify"
.PP
.Vb 1
\&    say "The error was: ",$@\->stringify;
.Ve
.PP
Formats the error as a human readable string.  Usually there's no
reason to call this directly, as it is used automatically if an
\&\f(CW\*(C`autodie::exception\*(C'\fR object is ever used as a string.
.PP
Child classes can override this method to change how they're
stringified.
.PP
\fIformat_default\fR
.IX Subsection "format_default"
.PP
.Vb 1
\&    my $error_string = $E\->format_default;
.Ve
.PP
This produces the default error string for the given exception,
\&\fIwithout using any registered message handlers\fR.  It is primarily
intended to be called from a message handler when they have
been passed an exception they don't want to format.
.PP
Child classes can override this method to change how default
messages are formatted.
.PP
\fInew\fR
.IX Subsection "new"
.PP
.Vb 7
\&    my $error = autodie::exception\->new(
\&        args => \e@_,
\&        function => "CORE::open",
\&        errno => $!,
\&        context => \*(Aqscalar\*(Aq,
\&        return => undef,
\&    );
.Ve
.PP
Creates a new \f(CW\*(C`autodie::exception\*(C'\fR object.  Normally called
directly from an autodying function.  The \f(CW\*(C`function\*(C'\fR argument
is required, its the function we were trying to call that
generated the exception.  The \f(CW\*(C`args\*(C'\fR parameter is optional.
.PP
The \f(CW\*(C`errno\*(C'\fR value is optional.  In versions of \f(CW\*(C`autodie::exception\*(C'\fR
1.99 and earlier the code would try to automatically use the
current value of \f(CW$!\fR, but this was unreliable and is no longer
supported.
.PP
Atrributes such as package, file, and caller are determined
automatically, and cannot be specified.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
autodie, autodie::exception::system
.SH LICENSE
.IX Header "LICENSE"
Copyright (C)2008 Paul Fenwick
.PP
This is free software.  You may modify and/or redistribute this
code under the same terms as Perl 5.10 itself, or, at your option,
any later version of Perl 5.
.SH AUTHOR
.IX Header "AUTHOR"
Paul Fenwick <pjf@perltraining.com.au>