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.\" ========================================================================
.\"
.IX Title "SEH 1"
.TH SEH 1 "2009-05-31" "perl v5.8.8" "User Contributed Perl Documentation"
.SH "NAME"
Exception::SEH \- rich try/catch/finally semantics without source filtering
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 10
\&        use Exception::SEH;
\&        try {
\&                <...> or die YourException;
\&        } catch (SomeException $e) {
\&                <catch code>
\&        } catch (YourException $e where { $_->param > 10 }) {
\&                log($e->message);
\&        } finally {
\&                <cleanup code>
\&        }
.Ve
.SH "FEATURES"
.IX Header "FEATURES"
.IP "\(bu" 2
Rich catch syntax
.IP "\(bu" 2
No need for trailing ; after try/catch/finally sequence
.IP "\(bu" 2
return from try/catch \- returns from subroutine, not just try/catch block
.IP "\(bu" 2
finally called in all cases (even after return)
.IP "\(bu" 2
@_ available for try block
.IP "\(bu" 2
Nested try/catch
.IP "\(bu" 2
Not a source filter (magic for syntax is provided by Devel::Declare)
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
.IP "try \s-1BLOCK\s0" 4
.IX Item "try BLOCK"
Evaluates \s-1BLOCK\s0, allowing any exceptions inside it to be caught and processed.
.IP "catch \s-1BLOCK\s0" 4
.IX Item "catch BLOCK"
.PD 0
.ie n .IP "catch ([[\s-1CLASS\s0] $VAR] [where \s-1BLOCK\s0]) \s-1BLOCK\s0" 4
.el .IP "catch ([[\s-1CLASS\s0] \f(CW$VAR\fR] [where \s-1BLOCK\s0]) \s-1BLOCK\s0" 4
.IX Item "catch ([[CLASS] $VAR] [where BLOCK]) BLOCK"
.PD
Catches and processes (using given \s-1BLOCK\s0) exception that (optionally) matches
some conditions. Rules to determine catch handler are following:
.RS 4
.IP "*" 2
Search is performed from beginning to end of 'catches' list
.IP "*" 2
First matched block is executed and the search is stopped
.IP "*" 2
If exception is not an object, then any condition with \s-1CLASS\s0 definition is skipped
.IP "*" 2
If condition has \s-1CLASS\s0, then \fB$@\-\fRisa(\s-1CLASS\s0)> is checked for true value
.IP "*" 2
If condition has 'where \s-1BLOCK\s0' part, then \s-1BLOCK\s0 is checked for true result, with \fB$_\fR assigned to caught exception
.IP "*" 2
catch \s-1BLOCK\s0, catch () \s-1BLOCK\s0, catch ($e) \s-1BLOCK\s0 are all the same and captures all possible exceptions
.IP "*" 2
If no condition matches throwed exception, then it's re-thrown (after \f(CW\*(C`finally\*(C'\fR is done)
.RE
.RS 4
.Sp
Inside \s-1BLOCK\s0 after \f(CW\*(C`catch\*(C'\fR exception is available as \fB$@\fR (always) and also as \f(CW$VAR\fR (lexical to \s-1BLOCK\s0),
if it was specified in \f(CW\*(C`catch\*(C'\fR signature.
.RE
.IP "finally \s-1BLOCK\s0" 4
.IX Item "finally BLOCK"
Finally block is always executed after either \f(CW\*(C`try\*(C'\fR or \f(CW\*(C`catch\*(C'\fR. Exception in it is available as \fB$@\fR.
.Sp
Note: if exception was generated inside a \f(CW\*(C`catch\*(C'\fR handler, than in \fB$@\fR would be new one, not
original from a \f(CW\*(C`try\*(C'\fR block.
.Sp
Note: \f(CW\*(C`exit\*(C'\fR and unhandled signals leads to immidiate program termination (latter even don't allow
global destruction to happen) \- in these cases, \f(CW\*(C`finally\*(C'\fR is \fBnot\fR called.
.IP "return \s-1EXPRESSION\s0" 4
.IX Item "return EXPRESSION"
\&\f(CW\*(C`return\*(C'\fR behaviour is modifiyed, so when you call it inside \f(CW\*(C`try\*(C'\fR/\f(CW\*(C`catch\*(C'\fR, it returns not from 
\&\f(CW\*(C`try\*(C'\fR block, but from the sub \f(CW\*(C`try\*(C'\fR was inside.
.Sp
Note: this does not apply to finally block.
.Sp
Note: if both \f(CW\*(C`catch\*(C'\fR and \f(CW\*(C`try\*(C'\fR uses \f(CW\*(C`return\*(C'\fR, than value from last \f(CW\*(C`return\*(C'\fR is used (but you
may ommit \f(CW\*(C`return\*(C'\fR in \f(CW\*(C`catch\*(C'\fR block, then return value is left unchanged).
.Sp
Note: argument for return is executed in the context of sub above \f(CW\*(C`try\*(C'\fR.
.Sp
Example:
.Sp
.Vb 7
\&        sub test{
\&                try{
\&                        return map { $_ * 2 } @_;
\&                }
\&        }
\&        $a = test(1, 2, 3);     #$a = 3
\&        @a = test(1, 2, 3);     #@a = (2, 4, 6)
.Ve
.IP "@_" 4
.IX Item "@_"
Inisde \f(CW\*(C`try\*(C'\fR, you have full read/write access to surronding sub's \f(CW@_\fR. 
.Sp
Note: inside \f(CW\*(C`catch\*(C'\fR/\f(CW\*(C`finally\*(C'\fR, you have only read-only access to \f(CW@_\fR.
.SH "CONFIGURATION"
.IX Header "CONFIGURATION"
When importing Exception::SEH to your module, you can specify
one or more of the following keywords: \fB\-nosig\fR \fB\-noret\fR \fB\-safetry\fR, which change default
behaviour in some way. These options are tracked on per-package basis.
.PP
.Vb 1
\&        use Exception::SEH -nosig, -safetry;
.Ve
.IP "\-nosig" 4
.IX Item "-nosig"
By default, Exception::SEH doesn't play with \f(CW$SIG\fR{_\|_DIE_\|_}, so your handler
is normally called. But if you need to suppress it inside try/catch/finally blocks,
you can import \f(CW\*(C`\-nosig\*(C'\fR.
.Sp
Note: if exception is re-thrown after \f(CW\*(C`finally\*(C'\fR block, _\|_DIE_\|_ handler is
always suppressed for that moment (so it is called only once
for each exception \- at first occurence).
.IP "\-safetry" 4
.IX Item "-safetry"
This options changes behaviour for uncaught exceptions after \f(CW\*(C`try\*(C'\fR block.
By default, they're re\-thrown, but with this option enabled \f(CW\*(C`try\*(C'\fR blocks are always safe \- just like \f(CW\*(C`eval\*(C'\fR.
.Sp
Note: this doesn't refer to exceptions occured in a \f(CW\*(C`catch\*(C'\fR and \f(CW\*(C`finally\*(C'\fR blocks.
.IP "\-noret" 4
.IX Item "-noret"
Tells Exception::SEH not to install \f(CW\*(C`return\*(C'\fR hook. This makes \f(CW\*(C`try\*(C'\fR blocks behave like
evals, and context for \f(CW\*(C`return\*(C'\fR is determined by context of \f(CW\*(C`try\*(C'\fR, not by context of sub,
containing \f(CW\*(C`try\*(C'\fR.
.SH "DIAGNOSTICS"
.IX Header "DIAGNOSTICS"
All compile-time discovered errors are raised through \f(CW\*(C`Carp::croak\*(C'\fR
with (hopefully) meaningful description.
.SH "CAVEATS"
.IX Header "CAVEATS"
Currently, three subroutines \- try, catch, finally \- are injected into caller's namespace.
.PP
Currently, it's impossible to use any other module that hooks \fB\s-1OP_RETURN\s0\fR \s-1OP\s0 on \s-1XS\s0 level \-
results are unpredictable. This may be fixed in future releases.
.PP
Currently, it's probably unsafe to place \f(CW\*(C`try\*(C'\fR/\f(CW\*(C`catch\*(C'\fR blocks around \f(CW\*(C`use\*(C'\fR/\f(CW\*(C`catch\*(C'\fR.
This needs further testing, and may be fixed in future releases.
.PP
Currently, due to way caller is detected, if you place try/catch/finally inside \f(CW\*(C`eval\*(C'\fR block,
\&\f(CW\*(C`return\*(C'\fR wouldn't work as expected. This will be fixed in future releases.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
TryCatch
.PP
Similar semantics, but it takes the whole Moose with itself \- often too much weight.
Currently lacks finally block and \fB@_\fR access inside try{}. But still, decent choice.
.PP
Exception::Class::TryCatch
.PP
Ugly syntax. Only Exception::Class\-derived exceptions.
.PP
Exception::Class::TCF
.PP
Better syntax. Lacks exception lexical in try block, returns from try{} block.
Still only Exception::Class\-derived exceptions.
.PP
Error::TryCatch
.PP
Source filter. No finally{} call after \fIreturn()\fR from try.
.PP
Error
.PP
\&\*(L"Error's syntactic sugar tends to break.\*(R" (c)
.SH "AUTHOR"
.IX Header "AUTHOR"
Sergey Aleynikov <sergey.aleynikov@gmail.com>
.SH "LICENSE"
.IX Header "LICENSE"
Copyright (c) 2009 by Sergey Aleynikov.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
.PP
Some part for parser are taken from Devel::Declare::Context::Simple, (c) Rhesa Rozendaal (?).
.PP
Idea how to set up return hook \- TryCatch, (c) Ash Berlin.