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.\" ========================================================================
.\"
.IX Title "Aspect::Advice::Before 3pm"
.TH Aspect::Advice::Before 3pm "2012-02-01" "perl v5.14.2" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.SH "NAME"
Aspect::Advice::Before \- Execute code before a function is called
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&  use Aspect;
\&  
\&  before {
\&  
\&      # Trace all calls to your module
\&      print STDERR "Called my function " . $_\->sub_name . "\en";
\&  
\&      # Shortcut calls to foo() to always be true
\&      if ( $_\->short_name eq \*(Aqfoo\*(Aq ) {
\&          return $_\->return_value(1);
\&      }
\&  
\&      # Add an extra flag to bar() but call as normal
\&      if ( $_\->short_name eq \*(Aqbar\*(Aq ) {
\&          $_\->args( $_\->args, \*(Aqflag\*(Aq );
\&      }
\&
\&  } call qr/^ MyModule::\ew+ $/
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \f(CW\*(C`before\*(C'\fR advice type is used to execute advice code prior to entry
into a target function. It is implemented by \fBAspect::Advice::Before\fR.
.PP
As well as creating side effects that run before the main code, the
\&\f(CW\*(C`before\*(C'\fR advice type is particularly useful for changing parameters or
shortcutting calls to functions entirely and replacing the value they
would normally return with a different value.
.PP
Please note that the \f(CW\*(C`highest\*(C'\fR pointcut (Aspect::Pointcut::Highest) is
incompatible with \f(CW\*(C`before\*(C'\fR. Creating a \f(CW\*(C`before\*(C'\fR advice with a pointcut
tree that contains a \f(CW\*(C`highest\*(C'\fR pointcut will result in an exception.
.PP
If speed is important to your program then \f(CW\*(C`before\*(C'\fR is particular
interesting as the \f(CW\*(C`before\*(C'\fR implementation is the only one that can take
advantage of tail calls via Perl's \f(CW\*(C`goto\*(C'\fR function, where the rest of the
advice types need the more costly Sub::Uplevel to keep \fIcaller()\fR returning
correctly.
.SH "AUTHORS"
.IX Header "AUTHORS"
Adam Kennedy <adamk@cpan.org>
.SH "COPYRIGHT AND LICENSE"
.IX Header "COPYRIGHT AND LICENSE"
Copyright 2010 Adam Kennedy.
.PP
This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.