Using DateTime together with Template::Toolkit

Corion has asked for the wisdom of the Perl Monks concerning the following question:

I am most likely looking in the wrong places and have missed some crucial piece of information. I can't get DateTime objects to play well with Template::Stash - the Template::Stash seems to want to compare the DateTime object against the template root, but the DateTime object does not want to be compared with anything other than a DateTime object, or something sufficiently similar. See my code below - it is some convoluted way of printing todays date, except it doesn't:

use strict;
use DateTime;
use Template;

my $config = {};
my $template = Template->new($config);
my $input = \'[% calendar.ymd(".") %]';

# process input template, substituting variables
$template->process($input, { calendar => DateTime->now })
    or die $template->error();
[download]

After patching DateTime.pm so it gives some better error diagnostics, I get

undef error - Cannot compare a datetime to a regular scalar (2005-02-2
+8T21:51:58 / Template::Stash=HASH(0x2048a14)) at c:/perl/site/5.8.5/l
+ib/Template/Stash.pm line 582
[download]

but I don't want to believe that nobody has used Template::Toolkit and DateTime together, so the error must be somewhere in my usage of one of the two.

Update: DateTime v0.28, Template::Toolkit 2.14

Update 2: I hacked myself a workaround by removing the overloaded string comparison of DateTime. This is horribly ugly and there must be a better way :-(

Comment on Using DateTime together with Template::Toolkit Select or Download Code

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Re: Using DateTime together with Template::Toolkit by friedo (Prior) on Feb 28, 2005 at 22:26 UTC
Update 2: I hacked myself a workaround by removing the overloaded string comparison of DateTime. This is horribly ugly and there must be a better way :-( Yes, that way is to not put method calls in templates. Is it really so hard to use the following? `my $input = \'[% calendar %]'; $template->process($input, { calendar => DateTime->now->ymd(".") } );` [download] I realize this is just a matter of style, but I really can't think of any good reason for such a simple operation not to occur in your program. Your program should assemble data, and your template should display it. (Caveat: For efficiency reasons, sometimes it's better to pass an iterator to a template instead of a fully constructed data structure. But this sort of thing should be the exception, not the rule, IMHO.)	[reply] [d/l]
Re^2: Using DateTime together with Template::Toolkit by lachoy (Parson) on Feb 28, 2005 at 23:03 UTC
I can think of a great reason not to do it: datetime formatting is a display issue, not a data issue. They should be kept separate as much as possible otherwise you start doing things like putting your HTML construction alongside your data access. Down that path lies a maintenance nightmare. Chris M-x auto-bs-mode	[reply]
Re^2: Using DateTime together with Template::Toolkit by Corion (Patriarch) on Feb 28, 2005 at 22:31 UTC
Of course, that could be a way to do it, but then, I like being able to make method/accessor calls on my objects - that's why I use Template::Toolkit and not HTML::Template. And I don't want to touch my precious Perl code just to change the formatting, especially for things as fragile as date separators.	[reply]
Re: Using DateTime together with Template::Toolkit by mdillon (Priest) on Mar 01, 2005 at 06:59 UTC
If you were using the XS Stash, I don't think this would be a problem. If you really have a reason to use the non-XS stash, you can patch TT. The fix is to change the code that creates the `$atroot` variable in the `_dotop` method. It is described in this post to the TT mailing list. There is similar code in `_assign` that could probably stand to be patched as well. Note: The change in question adds a dependency on the Scalar::Util module, which should work on whatever version of Perl you can run TT on.	[reply]
Re^2: Using DateTime together with Template::Toolkit by Corion (Patriarch) on Mar 01, 2005 at 07:27 UTC
I don't know resp. didn't check if the XS Stash is active or not, but it sure sounds like if it isn't. The patch you mentioned sounds promising - I will try that! Of course, there shouldn't be a difference between the XS version and the Pure Perl version of Template::Stash.	[reply]
Re^3: Using DateTime together with Template::Toolkit by mdillon (Priest) on Mar 01, 2005 at 15:55 UTC
I agree that they should work the same, but in this case, there is a discrepency. I only suggested using the XS Stash instead since it seems to work correctly. Also, that message was posted to the TT mailing list a few months ago (in response to a message from the maintainer, so he's obviously aware of it) and there hasn't been a release containing the fix yet. That makes me think that waiting for the pure Perl Stash to work may take a while.	[reply]
Re^3: Using DateTime together with Template::Toolkit by dragonchild (Archbishop) on Mar 01, 2005 at 13:57 UTC
Why not? They do different things ... Being right, does not endow the right to be rude; politeness costs nothing. Being unknowing, is not the same as being stupid. Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence. Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.	[reply]
Re: Using DateTime together with Template::Toolkit by mpeters (Chaplain) on Feb 28, 2005 at 21:58 UTC
That code snippet works just fine for me. DateTime 0.23 Template 2.14 Update: It also worked for me for DateTime 0.28	[reply]
Re: Using DateTime together with Template::Toolkit by lachoy (Parson) on Feb 28, 2005 at 23:06 UTC
Your code worked fine for me also: TT 2.10 and DateTime 0.20. (Wow, I gotta upgrade!) update: after upgrading to 2.14 and 0.28 it still worked okay. Did you build and are you using the XS TT stash? Chris M-x auto-bs-mode	[reply]