Re: String comparisons

I understand the dangers, but a string is a string and we developers are used to comparing strings since the times of strcmp.  Also I saw that in Environment we get the collator from the environment's locale, so the locale is clearly understood. Assuming it would be a bug is far from reality if you need to do some simple string sorting.

With string comparison I could do

<#if .now?string("yyyyMMdd") > "20130130">
After January 30 2013
</if>

And that is far from a bug.  The problem is, I am without .now?date > aDate?date, so I thought of going the string way, but then strings are restricted and this is what I have to do:

.now?string("yyyyMMdd")?date("yyyyMMdd")

To get a date with only the date portion.

Not very pretty.  Since I am writing a code generator, the results are very verbose, and perhaps internally inefficient.

Jaime

-----Original Message-----
From: Daniel Dekany [mailto:[email protected]] 
Sent: Wednesday, January 30, 2013 2:26 PM
To: FreeMarker-devel
Subject: Re: [Freemarker-devel] String comparisons

Wednesday, January 30, 2013, 10:43:30 PM, Jaime Garza wrote:

> In the code on ComparisonExpression:
>
>         else if(ltm instanceof TemplateScalarModel && rtm instanceof TemplateScalarModel) {
>             if(operation != EQUALS && operation != NOT_EQUALS) {
>                 throw new TemplateException("Can not use operator "
> + opString + " on string values.", env);
>             }
>             String first =
> EvaluationUtil.getString((TemplateScalarModel)ltm, left, env);
>             String second =
> EvaluationUtil.getString((TemplateScalarModel)rtm, right, env);
>             comp = env.getCollator().compare(first, second);
>         }
>
> Collator supports "less", "less than", "greater" and "greater than" semantics.
>
> What is the caveat on not allowing anything but equals and not equals?  There must be a reason.

The collators of the current locale(!) could be used technically (but with what settings?). But it's hard to find a reason to compare two strings in a template for anything but equality, so when FreeMarker runs into another kind of comparison, it's very likely that it's just the result of bug in the application. Typically, the user meant to compare two numbers or dates which come from XML or as HTTP request parameters, but have forgotten to parse them to number or date. A string comparison would silently give the wrong answer. It's dangerous, especially as there are cases where it accidentally gives the good answer, and that will happen while you are testing, of course... So it's better to throw an exception.

> (Having all the semantic behaviors would be a great way to deal with 
> date comparisons when I need to convert dates to text, and back to a 
> date.)

You want to compare dates in string form? I guess that happens to work with ISO dates... but not with most date formats.

> Thanks
> Jaime

--
Best regards,
 Daniel Dekany


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