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Date: Fri, 29 Sep 2017 12:29:01 +0000 (UTC)
From: "Daniel Dekany (JIRA)" <jira@apache.org>
To: notifications@freemarker.incubator.apache.org
Message-ID: <JIRA.13105893.1506638479000.235762.1506688141283@Atlassian.JIRA>
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Subject: [jira] [Comment Edited] (FREEMARKER-75) New built-in
 ?as("variableName") to store the left-hand operand to a variable.
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archived-at: Fri, 29 Sep 2017 12:29:05 -0000


    [ https://issues.apache.org/jira/browse/FREEMARKER-75?page=3Dcom.atlass=
ian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=3D1=
6185750#comment-16185750 ]=20

Daniel Dekany edited comment on FREEMARKER-75 at 9/29/17 12:28 PM:
-------------------------------------------------------------------

Regarding that {{?as}} should replace an existing variable. Maybe the sane =
way of combining this with FM2 is that {{?as\(x)}} declares a nested conten=
t variable (aka a loop variable), similarly to {{#list xs as x}} does. Othe=
rwise the scope is not obvious, like, if you have {{$\{expensiveExpression?=
as\(x)\}}} inside {{#function}}, will {{x}} be a local variable, or a templ=
ate namespace variable? (In FM3 I plan to use {{#var}} and {{#set}}, where =
the scope of the last depends on where {{#var}} was.) Anyway, this last doe=
sn't exactly helps the readability of the template ("Where does x coming fr=
om?" Looks for {{#assign}}-s for no avail...), so I probably wouldn't do th=
at it in FM3 either. The case where {{?as\(x)}} declares a nested content v=
ariable has a strong use case with {{#if}}, and the scope of the variable i=
s restricted, which hopefully makes this less confusing.


was (Author: ddekany):
Regarding that {{?as}} should replace an existing variable. Maybe the sane =
way of combining this with FM2 is that {{?as(x)}} declares a nested content=
 variable (aka a loop variable), similarly to {{#list xs as x}} does. Other=
wise the scope is not obvious, like, if you have {{$\{expensiveExpression?a=
s(x)\}}} inside {{#function}}, will {{x}} be a local variable, or a templat=
e namespace variable? (In FM3 I plan to use {{#var}} and {{#set}}, where th=
e scope of the last depends on where {{#var}} was.) Anyway, this last doesn=
't exactly helps the readability of the template ("Where does x coming from=
?" Looks for {{#assign}}-s for no avail...), so I probably wouldn't do that=
 it in FM3 either. The case where {{?as(x)}} declares a nested content vari=
able has a strong use case with {{#if}}, and the scope of the variable is r=
estricted, which hopefully makes this less confusing.

> New built-in ?as("variableName") to store the left-hand operand to a vari=
able.
> -------------------------------------------------------------------------=
-----
>
>                 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 =C5=BDi=C5=BEka
>
> 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=20
> {code}
> <#assign cached =3D (foo.bar.baz.expensiveCall())! >
> <#if cached?has_content() >
>      Hello, ${ cached }
> </#if>
> {code}
> In short, passing around the information that a value could not be obtain=
ed 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 simplifying, 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 conditi=
onal prefixes
> ${ expensive()?as("cached")!false + ", good bye!"?if(cached) }     // For=
 conditional suffixes
> ${ "Hi, ${expensive()?as("cached")!false}, again!"?if(cached) }     // Fo=
r conditional surrounding
> {code}
> The new {{?as()}} built-in could be also used for a more convenient way o=
f assigning wile printing:
> {code}
> ${"Hi ${user}"?as("greet")}.
> ${ greet }, again.
> {code}
> I hope my explanation does make sense.
> Thanks for considering.=20


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