[jira] [Created] (FREEMARKER-75) New built-in ?as("variableName") to store the left-hand operand to a variable.

["Ondra Žižka (JIRA)" <ji...@apache.org>]

Ondra Žižka created FREEMARKER-75:
-------------------------------------

             Summary: New built-in ?as("variableName") to store the left-hand operand to a variable.
                 Key: FREEMARKER-75
                 URL: https://issues.apache.org/jira/browse/FREEMARKER-75
             Project: Apache Freemarker
          Issue Type: New Feature
          Components: engine
    Affects Versions: 2.3.26-incubating
            Reporter: Ondra Žižka


When coding templates, one often runs into a situation like this:
{code}
<#if (foo.bar.baz.expensiveCall())!false >
     ${ foo.bar.baz.expensiveCall() }
</#if>
{code}
Solving it with currently available things is something like 
{code}
<#assign cached = (foo.bar.baz.expensiveCall())! >
<#if cached?has_content() >
     Hello, ${ cached }
</#if>
{code}
In short, passing around the information that a value could not be obtained is a bit cumbersome.

What I suggest is a built-in that would capture a value of an expression on the left to a new variable and pass it along.

{code}
<#if (foo.bar.baz.expensiveCall())!?as("cached")?has_content >
     Hello, ${ cached }
</#if>
{code}
The benefits is that there is need to compute the expression twice or do the assignment.

Speaking of simplicity, the expression above could also be simplified by another built-in, a "reversed" {{then()}}.  (For that I will file another jira.)

{code}
${ "Hi, "?if( expensive()?as("cached"), "") + cached }     // For conditional prefixes

${ expensive()?as("cached")!false + ", good bye!"?if(cached) }     // For conditional suffixes

${ "Hi, ${expensive()?as("cached")!false}, again!"?if(cached) }     // For conditional surrounding
{code}

The new {{?as()}} built-in could be also used for a more convenient way of assigning wile printing:
{code}
${"Hi ${user}"?as("greet")}.
${ greet }, again.
{code}

I hope my explanation does make sense.
Thanks for considering. 



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