comment on

I recently thought wantarray would allow me to create a useful Mason component that would either return data in an array so I could format it element by element -- or return a string of that data pre-formatted. Not a good idea. In fact, Mason components already have a dual nature about their return values -- so I think that adding a decision split in the return value just compounds the problem even more. Here is the Mason code:

<%init>
my @foo = $m->comp( '.foo' );
my $foo = $m->comp( '.foo' );
</%init>

<%def .foo>
<%init>
my @array = qw(foo bar baz);
return wantarray ? @array : join( '', map "$_<br/>", @array );
</%init>
</%def>
[download]

Now, so far there are no problems. @foo does contain the unformatted elements and $foo contains a string of the elements pre-formatted. As long as I only use those variable in my "template" then i will have no issue:

<!-- correct -->
<ol>
%for (@foo) {
    <li><% $_ %></li>
%}
</ol>
<!-- correct --> <p>foo = <% $foo %></p>
[download]

The problem comes when you try to take short cuts and call the component directly from your template. None of these do what you want:

<!-- incorrect --> <p>foo = <& .foo &></p>
<!-- incorrect --> <p>foo = <% $m->comp( '.foo' ) %></p>
<!-- incorrect --> <p>foo = <% $m->comp( '.foo' ) %></p>
[download]

The first is simply a wrong use of Mason* and the 2nd and 3rd return lists. This really is not a problem with wantarray so much as it is a trap that one thinks they can call Mason components in this manner -- and boy wouldn't it sure be great to utilize wantarray to make my call simple? Bzzzzzt. Here's the correct call:

<!-- correct -->   <p>foo = <% scalar $m->comp( '.foo' ) %></p>
[download]

* this usage is like calling a function that prints data to STDOUT, and our comp does not do this

Convoluted and confusing. One is really better off defining a "shared" array and two separate subs. One that is a true Mason component that only returns data, and the other a true Mason component that only SPITS OUT data:

<%def .get_foo>
<%init>
my @array = qw(foo bar baz);
return @array;
</%init>
</%def>
<%def .display_foo>
<% join( '', map "$_<br/>", $m->comp( '.get_foo' ) ) %>
</%def>
<!-- correct -->
<ol>
%for ($m->comp( '.get_foo' ) ) {
    <li><% $_ %></li>
%}
</ol>

<!-- correct --> <& .display_foo &>
[download]

I hope this adds some useful points to your excellent meditation.

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

In reply to Re: Use of wantarray Considered Harmful (Mason) by jeffa
in thread Use of wantarray Considered Harmful by kyle

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