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.\"
.IX Title "Template::Plugin::Assert 3pm"
.TH Template::Plugin::Assert 3pm "2018-11-02" "perl v5.28.0" "User Contributed Perl Documentation"
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.SH "NAME"
Template::Plugin::Assert \- trap undefined values
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    [% USE assert %]
\&    
\&    # throws error if any undefined values are returned
\&    [% object.assert.method %]
\&    [% hash.assert.key %]
\&    [% list.assert.item %]
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This plugin defines the \f(CW\*(C`assert\*(C'\fR virtual method that can be used
to automatically throw errors when undefined values are used.
.PP
For example, consider this dotop:
.PP
.Vb 1
\&    [% user.name %]
.Ve
.PP
If \f(CW\*(C`user.name\*(C'\fR is an undefined value then \s-1TT\s0 will silently ignore the 
fact and print nothing.  If you \f(CW\*(C`USE\*(C'\fR the \f(CW\*(C`assert\*(C'\fR plugin then you
can add the \f(CW\*(C`assert\*(C'\fR vmethod between the \f(CW\*(C`user\*(C'\fR and \f(CW\*(C`name\*(C'\fR elements,
like so:
.PP
.Vb 1
\&    [% user.assert.name %]
.Ve
.PP
Now, if \f(CW\*(C`user.name\*(C'\fR is an undefined value, an exception will be thrown:
.PP
.Vb 1
\&    assert error \- undefined value for name
.Ve
.SH "AUTHOR"
.IX Header "AUTHOR"
Andy Wardley <abw@wardley.org> <http://wardley.org/>
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (C) 2008 Andy Wardley.  All Rights Reserved.
.PP
This module is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Template::Plugin